Thermal insulation is important to facility operations, yet is often overlooked and undervalued. These materials can be used in either low- or high-temperature applications. For refinery and petrochemical plant applications, insulation materials can be classified into one of the three categories listed below:
• Granular
• Fibrous
• Cellular
1. Granular-type Insulations
Granular insulations are composed of small nodules that contain voids or hollow spaces. These materials are sometimes considered open-cell materials since gases can be transferred between the individual spaces. Calcium silicate and molded perlite insulations are considered granular insulations.
1.1 Calcium Silicate
Calcium silicate insulation is a rigid pipe and block insulation composed principally of calcium silicate and usually incorporates a fibrous reinforcement. It is intended for use in high temperature applications. If immersed in water at ambient temperatures, the material can absorb significant amounts of water (i.e. up to 400% by weight). Even when not immersed in water, the material can absorb up to 25% by weight water in high humidity conditions due to its hygroscopic nature. When exposed to water, the material has a pH of 9-10 and may be detrimental to coatings on metal surfaces. Additionally, some manufacturers offer products with controlled or low chloride levels for specialty applications. The advantages and disadvantages for calcium silicate insulation are listed below:
a) Advantages
- Low thermal conductivity (when dry)
- Suitable for temperatures to 1000°F (538°C) continuously or 1200°F (650°C) intermittently.
- Available in a variety of shapes/sizes
- Available with low chloride levels
b) Disadvantages
- Will readily absorb moisture
- Silica dust created during cutting may be carcinogenic
- Fragile (i.e. brittle). Care needed to avoid breakage during installation
1.2 Expanded Perlite
Perlite is a volcanic rock containing from 2 to 5 percent bonded water. It is a chemically inert substance composed basically of silica and aluminum. The perlite is expanded by means of rapid heating at a temperature between 1475°F and 2200°F (800°C and 1200°C). The vaporization of the bonded water and the formation of natural glass results in the expansion of the perlite particles. These particles have a granular shape.
Expanded perlite insulation is either rigid pipe or block insulation composed of expanded perlite, inorganic silicate binders, fibrous reinforcement, and silicone water-resistant additions. These silicone additions provide protection from water absorption at temperatures below 600°F (315°C). The water resistance of the material is reduced at or above this temperature. Similar to calcium silicate, some manufacturers offer expanded perlite products with controlled or low chloride levels for specialty applications. The advantages and disadvantages for expanded perlite insulation are listed below:
a) Advantages
- Water resistant up to 400°F (205°C)
- Good resistance to mechanical damage
- Available in a variety of shapes/sizes
b) Disadvantages
- Slightly more fragile than calcium silicate during installation
- Perlite dust can cause chronic poisoning
- Higher thermal conductivity than calcium silicate
2. Cellular-type Insulations
Cellular insulations are classified as either open cell structures where the cells are interconnecting, or closed cell structures where the cells are sealed from each other. Generally, materials that have greater than 90 percent closed-cell content are considered to be closed-cell materials.
2.1 Cellular Glass
Cellular glass (also referred to as foam glass) is a closed-cell insulation composed predominantly of silica-based glass. It is made by adding powdered carbon to crushed glass and firing the mixture to form a closed cell structure. It is commonly used on electric-traced or steam-traced piping for freeze protection or process control.
The low permeability and absorption characteristics of cellular glass make it an attractive choice for cold service and cryogenic applications. This insulation material does not wick water or liquids, and is used in hot service where the non-absorbent/non-wicking properties are desirable. The material has a thermal conductivity rating between mineral wool and calcium silicate, and displays good compressive strength. It can be friable and brittle when subjected to mechanical abuse, and can crack when subjected to large temperature differences and thermal shock.
Cellular glass has the chemical resistance of glass. Cellular glass systems have been designed for applications operating at temperatures from -450°F to 800°F (-260°C to 427°C). The material can suffer vibration-induced damage, and can also be prone to damage when boiling water is trapped between the pipe and the insulation. Stress relief cracking of cellular glass can also occur at service temperatures above 450°F to 500°F (230°C to 270°C). The manufacturer should be consulted for the best method for insulating systems operating above 450°F (230°C).
The advantages and disadvantages for cellular glass insulation are listed below:
a) Advantages
- Does not absorb water
- High resistance to mechanical damage when jacketed
- Thermal conductivity does not deteriorate with aging
b) Disadvantages
- Susceptible to thermal shock if temperature gradient >300°F (>150°C)
- Easily abrades in vibrating service, and fragile before application
- Higher price when compared to other insulation types
2.2 Organic Foams
This category of insulation materials includes polyurethane, polyisocyanurate, flexible elastomeric, polystyrene, and phenolic insulations. Except for flexible elastomeric insulation, they are classified as either rigid/closed-cell foams or flexible/closed-cell foams. Flexible elastomeric insulation is classified as an a flexible/closed-cell foam. These materials contain chlorides, fluorides, silicates, and sodium ions which can be leached from the insulation at temperatures above 212°F (100°C). The leachate produced can have a wide range of pH (i.e. 1.7 to 10.0). Accelerated corrosion can take place when the pH of the leachate is below 6.0.
2.2.1 Polyurethane Foam
Polyurethane foam is an organic, closed-cellular foam that can be installed by spraying or casting in the shop or field. Pre-cast pieces are also available. Closed-cell foams are structures where all of the tiny foam cells are packed close together with no interconnected pores. The foam cells are filled with a low-conductivity gas, usually hydrochlorofluorocarbon (HCFC), which helps the foam to rise and expand. It is an insulation product that is produced on-site, and is typically applied by certified applicators. Two liquid components, an organic isocyanate compound (i.e. diisocyanate) and an alcohol (i.e. polyol) are mixed at high or low pressure using a spray gun with the reacting mix being sprayed onto the substrate to provide a seamless seal.
Polyurethane foam is frequently used for pre-insulated pipe joints. It has low permeability and absorption characteristics, but can absorb water after prolonged service. A typical design range for polyurethane foam is from -150°F to 275°F (-65°C to 135°C). The advantages and disadvantages for polyurethane foam insulation are listed below:
a) Advantages
- Low permeability and absorption characteristics (closed cell)
- Multiple product forms and easy to apply in the field
- Provides a seamless seal
b) Disadvantages
- Can be ignited and release toxic gases if exposed to an open flame.
- Sensitivity to UV radiation (sunlight)
- Can be vulnerable to some acids, caustics, solvents, hydrocarbons, and other chemicals
2.2.2 Polystyrene Foam
There are two categories of polystyrene foam insulation, 1) expanded polystyrene foam (EPS), and 2) extruded polystyrene foam (XPS).
Expanded polystyrene (EPS) foam is a closed-cell insulation that is manufactured by expanding a polystyrene polymer. It is usually white, and made of pre-expanded polystyrene beads. It is an aromatic, thermoplastic polymer made from the monomer styrene which is in solid (glassy) state at room temperature. When heated above 212°F (100°C), it flows sufficiently to permit molding or extrusion, becoming a solid when cooled.
Extruded polystyrene (XPS) is a rigid, closed-cell insulation manufactured from solid polystyrene crystals. The crystals are fed into an extruder along with special additives and a blowing agent and melted into a viscous plastic fluid. After being forced through the extrusion die, the hot, thick liquid expands to become a foam which is shaped, cooled, and trimmed to dimension. This continuous extrusion process produces a uniform closed-cell structure with a smooth continuous skin.
The advantages and disadvantages for polystyrene foam insulation are listed below:
a) Advantages
- Excellent resistance to water and water absorption from freeze/thaw cycling
- Very stable and does not biodegrade for hundreds of years
- Resistant to photolysis
b) Disadvantages
- Like other organic compounds, polystyrene is flammable.
- When burned without enough oxygen or at lower temperatures, polystyrene can produce a number of chemicals including polycyclic aromatic hydrocarbons, carbon black, and carbon monoxide, as well as styrene monomers which can irritate eyes, nose, and respiratory system.
- Primarily a cold system insulation material, melting point is approximately 465°F (240°C).
2.2.3 Polyisocyanurate Foam
Polyisocyanurate is an organic, closed-cellular, rigid foam. It has low permeability and absorption characteristics, and is typically used in cold service applications. The material is flexible and has reasonable strength to provide resistance to light physical abuse. It has a lower thermal conductivity than mineral wool insulations. A typical design temperature range is -297°F to 300°F (-150°C to 150°C). Disadvantages include combustibility and sensitivity to UV radiation (sunlight). Combustion may release toxic gases. Chemical resistance is generally good but can be vulnerable some acids, caustics, solvents, hydrocarbons and other. The advantages and disadvantages for of polyisocyanurate foam insulation are listed below:
a) Advantages
- Low permeability and absorption characteristics
- Multiple product forms and easy to apply in the field
b) Disadvantages
- Like other organic compounds, polyisocyanurate is flammable.
- Primarily a cold system insulation material
- When burned without enough oxygen or at lower temperatures, a number of chemicals are produced which can irritate eyes, nose, and respiratory system
3. Fibrous-type Insulations
This category of insulation materials includes mineral wool and fiberglass insulation. These materials are processed from molten state into fibrous form and combined with organic binders and pressed into rolls or sheets. The fiber length, fiber orientation, and type of binder used impact the ability of these materials to repel water. Upon breakdown of the binder, the wicking ability of these materials increases significantly and transmits moisture or corrosive solutions to the underlying surface. Mineral wools are unattractive to rodents but will provide a structure for bacterial growth if allowed to become wet.
3.1. Mineral Fiber
Mineral fiber insulations are composed principally of fibers manufactured from rock, slag, or glass, with or without binders. Molten glass, stone or slag is spun into a fiber-like structure. Inorganic rock or slag is the main components (typically 98%) of stone wool. The remaining 2% organic content is generally a thermosetting resin binder (an adhesive) and a little oil. Though the individual fibers conduct heat very well, when pressed into rolls and sheets their ability to partition air makes them excellent heat insulators and sound absorbers. Mineral fiber insulation is commonly used in hot applications up to 1200°F (650°C). Mineral fiber has a lower thermal conductivity than calcium silicate and perlite. However, even with metal jacketing, mineral fiber is subject to mechanical damage due to its low compressive strength and lack of resiliency. This can lead to reduced insulation thickness and possibly open jacket seams where the jacket has been crimped. If used at an elevated temperature, the organic binder that helps to hold the fibrous insulation together is burned away causing a further reduction in strength.
Fibrous insulations are readily permeable to vapors and liquids. For this reason, fibrous insulation is not used alone for low temperature applications where condensation can occur. Most fibers will readily wick hydrocarbons and water. Sometimes hydrophobic treatments or coatings are applied to the insulation by manufacturer to reduce water absorption and wicking. These coatings do not eliminate water saturation when immersed and the coating effectiveness may degrade in-service after exposure to higher temperatures.
The advantages and disadvantages for mineral wool insulation are listed below:
a) Advantages
- Used in hot applications up to 1200°F (650°C)
- Has a lower thermal conductivity than calcium silicate and perlite
- Low leachable chloride content (< 5ppm)
b) Disadvantages
- Fibrous insulations are readily permeable to vapors and liquids.
- Most fibers will readily wick hydrocarbons and water
- Mineral fiber is subject to mechanical damage due to its low compressive strength and lack of resiliency
3.2. Fiberglass
Fiberglass is widely used as industrial insulation. Fiberglass is mechanically weak like mineral fiber and shares the same disadvantages with respect to wicking and permeability. Maximum use temperature is typically less than 850°F (455°C) with some users specifying a temperature maximum of 450°F (230°C) due to binder burnout. The advantages and disadvantages for fiberglass insulation are listed below:
a) Advantages
- Noncombustible
b) Disadvantages
- Compressing the material reduces its effectiveness
- Absorbs water
- Can cause skin allergies
3.3. Silica Aerogel
Silica aerogel is a synthetically produced amorphous silica gel which is distinctly different from crystalline silica. It is impregnated into a non-woven flexible fabric substrate (i.e. batting) for reinforcement. Aerogels are good thermal insulators because they almost nullify convective, conductive, and radiative heat transfer. Silica aerogels have an extremely low thermal conductivity ranging from 0.03 W/m·K to 0.004 W/m·K which correspond to R-values of 14 to 105 for 3.5 inch thickness. Product forms can be as a flexible mat/blanket and include integral vapor barriers. The advantages and disadvantages for silica aerogel insulation are listed below:
a) Advantages
- Highest thermal performance of any insulating material known
- Significantly reduced thickness for equivalent performance to other insulating systems
- Wide range of temperature applications (may require a change in specific product to cover hot or cold insulation)
b) Disadvantages
- Aerogels are typically hygroscopic
- Need chemical treatment to be hydrophobic
- Typically higher cost of materials (installed cost and performance may provide economic benefits in long run)
• Granular
• Fibrous
• Cellular
1. Granular-type Insulations
Granular insulations are composed of small nodules that contain voids or hollow spaces. These materials are sometimes considered open-cell materials since gases can be transferred between the individual spaces. Calcium silicate and molded perlite insulations are considered granular insulations.
1.1 Calcium Silicate
Calcium silicate insulation is a rigid pipe and block insulation composed principally of calcium silicate and usually incorporates a fibrous reinforcement. It is intended for use in high temperature applications. If immersed in water at ambient temperatures, the material can absorb significant amounts of water (i.e. up to 400% by weight). Even when not immersed in water, the material can absorb up to 25% by weight water in high humidity conditions due to its hygroscopic nature. When exposed to water, the material has a pH of 9-10 and may be detrimental to coatings on metal surfaces. Additionally, some manufacturers offer products with controlled or low chloride levels for specialty applications. The advantages and disadvantages for calcium silicate insulation are listed below:
a) Advantages
- Low thermal conductivity (when dry)
- Suitable for temperatures to 1000°F (538°C) continuously or 1200°F (650°C) intermittently.
- Available in a variety of shapes/sizes
- Available with low chloride levels
b) Disadvantages
- Will readily absorb moisture
- Silica dust created during cutting may be carcinogenic
- Fragile (i.e. brittle). Care needed to avoid breakage during installation
1.2 Expanded Perlite
Perlite is a volcanic rock containing from 2 to 5 percent bonded water. It is a chemically inert substance composed basically of silica and aluminum. The perlite is expanded by means of rapid heating at a temperature between 1475°F and 2200°F (800°C and 1200°C). The vaporization of the bonded water and the formation of natural glass results in the expansion of the perlite particles. These particles have a granular shape.
Expanded perlite insulation is either rigid pipe or block insulation composed of expanded perlite, inorganic silicate binders, fibrous reinforcement, and silicone water-resistant additions. These silicone additions provide protection from water absorption at temperatures below 600°F (315°C). The water resistance of the material is reduced at or above this temperature. Similar to calcium silicate, some manufacturers offer expanded perlite products with controlled or low chloride levels for specialty applications. The advantages and disadvantages for expanded perlite insulation are listed below:
a) Advantages
- Water resistant up to 400°F (205°C)
- Good resistance to mechanical damage
- Available in a variety of shapes/sizes
b) Disadvantages
- Slightly more fragile than calcium silicate during installation
- Perlite dust can cause chronic poisoning
- Higher thermal conductivity than calcium silicate
2. Cellular-type Insulations
Cellular insulations are classified as either open cell structures where the cells are interconnecting, or closed cell structures where the cells are sealed from each other. Generally, materials that have greater than 90 percent closed-cell content are considered to be closed-cell materials.
2.1 Cellular Glass
Cellular glass (also referred to as foam glass) is a closed-cell insulation composed predominantly of silica-based glass. It is made by adding powdered carbon to crushed glass and firing the mixture to form a closed cell structure. It is commonly used on electric-traced or steam-traced piping for freeze protection or process control.
The low permeability and absorption characteristics of cellular glass make it an attractive choice for cold service and cryogenic applications. This insulation material does not wick water or liquids, and is used in hot service where the non-absorbent/non-wicking properties are desirable. The material has a thermal conductivity rating between mineral wool and calcium silicate, and displays good compressive strength. It can be friable and brittle when subjected to mechanical abuse, and can crack when subjected to large temperature differences and thermal shock.
Cellular glass has the chemical resistance of glass. Cellular glass systems have been designed for applications operating at temperatures from -450°F to 800°F (-260°C to 427°C). The material can suffer vibration-induced damage, and can also be prone to damage when boiling water is trapped between the pipe and the insulation. Stress relief cracking of cellular glass can also occur at service temperatures above 450°F to 500°F (230°C to 270°C). The manufacturer should be consulted for the best method for insulating systems operating above 450°F (230°C).
The advantages and disadvantages for cellular glass insulation are listed below:
a) Advantages
- Does not absorb water
- High resistance to mechanical damage when jacketed
- Thermal conductivity does not deteriorate with aging
b) Disadvantages
- Susceptible to thermal shock if temperature gradient >300°F (>150°C)
- Easily abrades in vibrating service, and fragile before application
- Higher price when compared to other insulation types
2.2 Organic Foams
This category of insulation materials includes polyurethane, polyisocyanurate, flexible elastomeric, polystyrene, and phenolic insulations. Except for flexible elastomeric insulation, they are classified as either rigid/closed-cell foams or flexible/closed-cell foams. Flexible elastomeric insulation is classified as an a flexible/closed-cell foam. These materials contain chlorides, fluorides, silicates, and sodium ions which can be leached from the insulation at temperatures above 212°F (100°C). The leachate produced can have a wide range of pH (i.e. 1.7 to 10.0). Accelerated corrosion can take place when the pH of the leachate is below 6.0.
2.2.1 Polyurethane Foam
Polyurethane foam is an organic, closed-cellular foam that can be installed by spraying or casting in the shop or field. Pre-cast pieces are also available. Closed-cell foams are structures where all of the tiny foam cells are packed close together with no interconnected pores. The foam cells are filled with a low-conductivity gas, usually hydrochlorofluorocarbon (HCFC), which helps the foam to rise and expand. It is an insulation product that is produced on-site, and is typically applied by certified applicators. Two liquid components, an organic isocyanate compound (i.e. diisocyanate) and an alcohol (i.e. polyol) are mixed at high or low pressure using a spray gun with the reacting mix being sprayed onto the substrate to provide a seamless seal.
Polyurethane foam is frequently used for pre-insulated pipe joints. It has low permeability and absorption characteristics, but can absorb water after prolonged service. A typical design range for polyurethane foam is from -150°F to 275°F (-65°C to 135°C). The advantages and disadvantages for polyurethane foam insulation are listed below:
a) Advantages
- Low permeability and absorption characteristics (closed cell)
- Multiple product forms and easy to apply in the field
- Provides a seamless seal
b) Disadvantages
- Can be ignited and release toxic gases if exposed to an open flame.
- Sensitivity to UV radiation (sunlight)
- Can be vulnerable to some acids, caustics, solvents, hydrocarbons, and other chemicals
2.2.2 Polystyrene Foam
There are two categories of polystyrene foam insulation, 1) expanded polystyrene foam (EPS), and 2) extruded polystyrene foam (XPS).
Expanded polystyrene (EPS) foam is a closed-cell insulation that is manufactured by expanding a polystyrene polymer. It is usually white, and made of pre-expanded polystyrene beads. It is an aromatic, thermoplastic polymer made from the monomer styrene which is in solid (glassy) state at room temperature. When heated above 212°F (100°C), it flows sufficiently to permit molding or extrusion, becoming a solid when cooled.
Extruded polystyrene (XPS) is a rigid, closed-cell insulation manufactured from solid polystyrene crystals. The crystals are fed into an extruder along with special additives and a blowing agent and melted into a viscous plastic fluid. After being forced through the extrusion die, the hot, thick liquid expands to become a foam which is shaped, cooled, and trimmed to dimension. This continuous extrusion process produces a uniform closed-cell structure with a smooth continuous skin.
The advantages and disadvantages for polystyrene foam insulation are listed below:
a) Advantages
- Excellent resistance to water and water absorption from freeze/thaw cycling
- Very stable and does not biodegrade for hundreds of years
- Resistant to photolysis
b) Disadvantages
- Like other organic compounds, polystyrene is flammable.
- When burned without enough oxygen or at lower temperatures, polystyrene can produce a number of chemicals including polycyclic aromatic hydrocarbons, carbon black, and carbon monoxide, as well as styrene monomers which can irritate eyes, nose, and respiratory system.
- Primarily a cold system insulation material, melting point is approximately 465°F (240°C).
2.2.3 Polyisocyanurate Foam
Polyisocyanurate is an organic, closed-cellular, rigid foam. It has low permeability and absorption characteristics, and is typically used in cold service applications. The material is flexible and has reasonable strength to provide resistance to light physical abuse. It has a lower thermal conductivity than mineral wool insulations. A typical design temperature range is -297°F to 300°F (-150°C to 150°C). Disadvantages include combustibility and sensitivity to UV radiation (sunlight). Combustion may release toxic gases. Chemical resistance is generally good but can be vulnerable some acids, caustics, solvents, hydrocarbons and other. The advantages and disadvantages for of polyisocyanurate foam insulation are listed below:
a) Advantages
- Low permeability and absorption characteristics
- Multiple product forms and easy to apply in the field
b) Disadvantages
- Like other organic compounds, polyisocyanurate is flammable.
- Primarily a cold system insulation material
- When burned without enough oxygen or at lower temperatures, a number of chemicals are produced which can irritate eyes, nose, and respiratory system
3. Fibrous-type Insulations
This category of insulation materials includes mineral wool and fiberglass insulation. These materials are processed from molten state into fibrous form and combined with organic binders and pressed into rolls or sheets. The fiber length, fiber orientation, and type of binder used impact the ability of these materials to repel water. Upon breakdown of the binder, the wicking ability of these materials increases significantly and transmits moisture or corrosive solutions to the underlying surface. Mineral wools are unattractive to rodents but will provide a structure for bacterial growth if allowed to become wet.
3.1. Mineral Fiber
Mineral fiber insulations are composed principally of fibers manufactured from rock, slag, or glass, with or without binders. Molten glass, stone or slag is spun into a fiber-like structure. Inorganic rock or slag is the main components (typically 98%) of stone wool. The remaining 2% organic content is generally a thermosetting resin binder (an adhesive) and a little oil. Though the individual fibers conduct heat very well, when pressed into rolls and sheets their ability to partition air makes them excellent heat insulators and sound absorbers. Mineral fiber insulation is commonly used in hot applications up to 1200°F (650°C). Mineral fiber has a lower thermal conductivity than calcium silicate and perlite. However, even with metal jacketing, mineral fiber is subject to mechanical damage due to its low compressive strength and lack of resiliency. This can lead to reduced insulation thickness and possibly open jacket seams where the jacket has been crimped. If used at an elevated temperature, the organic binder that helps to hold the fibrous insulation together is burned away causing a further reduction in strength.
Fibrous insulations are readily permeable to vapors and liquids. For this reason, fibrous insulation is not used alone for low temperature applications where condensation can occur. Most fibers will readily wick hydrocarbons and water. Sometimes hydrophobic treatments or coatings are applied to the insulation by manufacturer to reduce water absorption and wicking. These coatings do not eliminate water saturation when immersed and the coating effectiveness may degrade in-service after exposure to higher temperatures.
The advantages and disadvantages for mineral wool insulation are listed below:
a) Advantages
- Used in hot applications up to 1200°F (650°C)
- Has a lower thermal conductivity than calcium silicate and perlite
- Low leachable chloride content (< 5ppm)
b) Disadvantages
- Fibrous insulations are readily permeable to vapors and liquids.
- Most fibers will readily wick hydrocarbons and water
- Mineral fiber is subject to mechanical damage due to its low compressive strength and lack of resiliency
3.2. Fiberglass
Fiberglass is widely used as industrial insulation. Fiberglass is mechanically weak like mineral fiber and shares the same disadvantages with respect to wicking and permeability. Maximum use temperature is typically less than 850°F (455°C) with some users specifying a temperature maximum of 450°F (230°C) due to binder burnout. The advantages and disadvantages for fiberglass insulation are listed below:
a) Advantages
- Noncombustible
b) Disadvantages
- Compressing the material reduces its effectiveness
- Absorbs water
- Can cause skin allergies
3.3. Silica Aerogel
Silica aerogel is a synthetically produced amorphous silica gel which is distinctly different from crystalline silica. It is impregnated into a non-woven flexible fabric substrate (i.e. batting) for reinforcement. Aerogels are good thermal insulators because they almost nullify convective, conductive, and radiative heat transfer. Silica aerogels have an extremely low thermal conductivity ranging from 0.03 W/m·K to 0.004 W/m·K which correspond to R-values of 14 to 105 for 3.5 inch thickness. Product forms can be as a flexible mat/blanket and include integral vapor barriers. The advantages and disadvantages for silica aerogel insulation are listed below:
a) Advantages
- Highest thermal performance of any insulating material known
- Significantly reduced thickness for equivalent performance to other insulating systems
- Wide range of temperature applications (may require a change in specific product to cover hot or cold insulation)
b) Disadvantages
- Aerogels are typically hygroscopic
- Need chemical treatment to be hydrophobic
- Typically higher cost of materials (installed cost and performance may provide economic benefits in long run)
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