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Last edited 10 Sep 2024

Types of rigid foam insulation

[edit] Introducing rigid foam insulation

Whilst not all rigid foam products are derived of plastic or chemically based, there are many that are and as such represent just a few of the types of plastic used in construction. The petroleum or plastic derived rigid foam insulants alone represent a broad range of material types, that vary widely, whilst there are also a number of other organic and mineral based options.

Rigid foam insulation is most often a closed-cell form of insulation; that is, it is formed by creating a series of closed bubbles of gas within the chemical and often oil-derived material, thus reducing thermal conductivity to a minimum. There are a variety of generic rigid foam insulants with different basic ingredients in terms of chemical compositions, with a wider variety of specific products that may vary in density, chemical make-up, and the processes involved in their product ion, as well as impact and performance. Individual products should be thoroughly investigated before being specified.

The differences between individual products may include the employment of different blowing agents (sometimes referred to as pneumatogens), which are used to create the air pockets or cellular structure, additives or coatings that help improve certain properties such as flow during processing and pre-expansion, how the material cools, as well as fire retardants.

When looking at any specific product,third-party certification should be sought both in terms of in-use performance, such as fire, as well as environmental impact.

Below are some more common rigid foam insulants, in part with an indication of the additives used. Other types of rigid insulation materials are also available; some are foam-related but not oil-based, while others are cellular in structure but not foam-based, such as glass insulation. Bio-based insulation materials are also available and have natural cell structures that trap air.

[edit] Some advantages of rigid foam insulation

Generally, they have very low conductivity with good insulating properties, outperforming many other insulants in terms of the thickness required to meet certain insulation levels.
They are closed cells and, as such, normally perform well under damp, moist, and wet conditions.
They are very light, making them easy to transport and install.
They can be mass produced at relatively low costs in relation to performance.
They are chemical-based and, as such, not generally tied to any particular location, and raw materials are small in size and thus can be transported at relatively low cost.
They are generally inert and pose little threat to health through installation (this is sometimes contested, and protection is often recommended during processing, cutting, and installation).
They are generally inert and plastic-based, and so they take a significant amount of time to break down or fail.
Some of these chemical-based insulants are technically recyclable, but the practicality of recycling in reality means many are not.
Additives and processing can help improve the performance of such materials in fire-related scenarios.
In some cases, the introduction of recycled plastic content diverted from other streams has proven to be successful, for example, PET, though this is unlikely to be more than 50% by content.

[edit] Some disadvantages of rigid foam insulants

They are complex materials, often with a variety of additives that can significantly affect performance, such as under fire conditions or environmental impacts. Furthermore, many materials look very similar, and thus it can be impossible to tell through visual inspection the make-up of the products. As such, third-party certification can be crucial.
It has been argued that some foam materials or specific additives may be detrimental to health when installed internally through the release of volatile organic compounds (VOCs), though not in all cases.
It has been argued that some foam materials or specific additives may be detrimental to health through the installation process, for example, in the dust created through cold cutting or gases released, such as phenylethene fumes, through hot wire cutting.
Some additives used in foam materials, such as to improve performance in fire, may pose a threat through bioaccumulation in the environment, such as persistent organic pollutants (POPs), for example, hexabromocyclododecane (HBCD). However, increasing legislation warning about or banning such chemicals means some products (but not all) avoid their use. Individual products should be checked.
Some additives used in foam materials, such as to improve performance in fire, may include per- and polyfluorinated alkyl substances (PFAS's), also referred to as forever chemicals. These can pose a threat through bioaccumulation in the environment as well as in humans. Again, individual products should be checked.
As the basic ingredients and the foam materials themselves can be mass produced relatively easily, controlling the production sources of raw materials and the impact at the various stages of the supply chain can become complex.
Although some of the materials can be recycled, in many cases, because of contamination through use and functioning collection schemes, the recycling of such materials can be difficult.
The specification of all rigid foam insulation in relation to fire safety has come under increasing scrutiny, not only in terms of fire resistance but also off-gases (particularly hydrogen cyanide) under burning scenarios. The primary rigid foam insulation used on the Grenfell Tower building was a specific product of the polyisocyanurate (PIR) insulation, although polyethylene was also present in the cladding material sandwiched between aluminium sheets.

[edit] Types of rigid foam insulation

[edit] Expanded Polystyrene (EPS)

EPS foam insulation is a polystyrene product that uses a blowing agent (also called pneumatogens), most commonly pentane, to produce a closed cellular structure made primarily of air. Blowing agents work in a variety of ways, mechanically, physically, chemically, or in combination. Applied to the liquid polystyrene material, the cellular structure created increases thermal and acoustic insulation, as well as its stiffness, reducing density. Sometimes called Styrofoam, this is a lightweight, rigid foam board made from expanded polystyrene beads with a low U value, moisture resistance, and versatility. It is commonly used in walls, roofs, and foundations.

Polystyrene is made by stringing together, or polymerizing, styrene, a building block chemical used in the manufacture of many products. Natural styrene occurs in small amounts in foods such as strawberries, cinnamon, coffee, peanuts, and beef. Polystyrene is normally derived from synthetic styrene, which is made from ethylbenzene, which is a monocyclic aromatic hydrocarbon and a key product in the petrochemical industry.

To improve its performance, fire retardants may be added, such as hexabromocyclododecane (HBCD). In the early 2000's, HBCD was added to the Stockholm Convention list of persistent organic pollutants, which started with 12, known as the dirty dozen, and later expanded to more than 20.

Although polystyrene can be classified as either a thermoset plastic or a thermoplastic, EPS is classified as a thermoplastic, meaning it can, in theory, be melted down and recycled so long as any site contamination and collection issues are overcome.

[edit] Extruded Polystyrene (XPS)

XPS foam insulation is very similar to EPS but is in some ways a higher-quality, denser product, so it is more hard-wearing and water-resistant with equal or better insulating qualities. It is often used in applications where moisture resistance and some strength are important, such as below-ground or below slabs.

XPS is made by heating polystyrene resin beads or granules to a high temperature in an extruder. Blowing agents are added, along with colouring agents, to create a denser, closed cellular structure. Common blowing agents used to produce XPS have included hydrofluorocarbons (HFC-134a and 142b). However, much of the industry has moved away from the use of hydrofluorocarbons (HFCs). HFC-134a, for example, has a GWP of 1,430, meaning it traps 1,430 times as much heat as carbon dioxide does over 100 years. Other options also exist, such as blends that contain hydrofluoroolefins (HFOs).

In the 1980s, chlorofluorocarbons (CFCs), which had both high ozone depletion (OD) and global warming potential(GWP), were replaced by hydrochlorofluorocarbons (HCFCs), which also depleted the ozone layer and had high GWP,but to a lesser degree. These were then replaced by hydrofluorocarbons (HFCs), which had minimal effect on the ozone layer but were potent greenhouse gases. In some cases, these have been replaced by hydrochlorofluoroolefins (HFOs), sometimes used in combination with pentane. Hydrochlorofluoroolefin is generally accepted as having far less environmentally damaging potential. The main variations used are HFO-1234yf, HFO-1234ze, and HCFO-1233zd, and while there are some criticisms regarding some of the variants it is currently considered the better alternative.

Importantly, although polystyrene can be classified as either a thermoset plastic or a thermoplastic, XPS is classified as a thermoplastic, meaning it can in theory be melted down and recycled so long as any site contamination and collection issues are overcome.

[edit] Graphite Polystyrene (GPS)

GPS has a polymer matrix that contains graphite. The high-purity graphite particles are introduced into the raw material, polystyrene beads, which are heated at high temperatures and then treated with steam to create the cellularly dense structure in a similar way to standard polystyrene. The inclusion of graphite particles helps to increase the foam's resistance to the flow of heat by reflecting heat energy to a greater extent than standard polystyrene.

In terms of fire, there is some evidence that graphite can improve resistance to the spread of fire, while other studies have also looked at Expanded Graphite Coating on Polystyrene Bead for Improving Flame Retardancy. The indication is that most graphite polystyrenes are also treated with a fire retardant, although this is unclear and may vary from product to product.

[edit] Rigid Polyurethane (PUR, PU or RPUF)

Polyurethane foam (PUR, PU) can have either an open-cellular structure or a closed-cellular structure, with the former being mostly used internally. It can be a thermoplastic or thermoset elastomer, depending on how it reacts to heat in general. PUR foam is a thermoset elastomer, so strictly speaking, it is not a plastic as such. The long, flexible polymermolecules that comprise thermoset polyurethanes make them true elastomers.

As a polymer, it is formed by the reaction of a diisocyanate or polymeric isocyanate with polyols (an alcohol with more than two reactive hydroxyl groups per molecule) in the presence of suitable catalysts and additives. Amine catalysts or blowing catalysts, especially tertiary amines, are the most common organic base catalysts in the synthesis of polyurethanes, although organotin catalysts are also used. Isocyanates and polyols are both products that are derived from crude oil; polyols may also be made of natural oils from renewable sources. When these ingredients are mixed, a foaming reaction occurs between polyisocyanate and water, forming carbamic acid, which then decomposes to form carbon dioxide (CO2) and an amine group. The carbon dioxide gas is responsible for blowing the polymer into foam.

Fully-cured polyurethane products are inert and non-toxic. The properties of polyurethane are influenced by the types of isocyanates and polyols used to make them. They can range from tough or rigid materials to flexible materials. Insulation can also be in a rigid or flexible form. As such, it can be used to make products that are both strong and lightweight, as well as durable and highly versatile. It is a key ingredient in several types of high-efficiency insulation materials (such as rigid foam insulation panels). For more information, see Polyurethane spray foam is used in structurally insulated panels and composite structures. It is also used for paints and other coatings, microcellular foam seals and gaskets, wheels and tyres, sealants, binders, and adhesives.

Melamine is often used in polyurethane foam as a fire retardant, but other halogen-containing flame retardants such as chlorine, bromine, fluorine, and iodine containing chemical groups may be used.

[edit] Polyisocyanurate (PIR or Polyiso)

PIR foam insulation is known for its high thermal resistance, but it has recently come under great scrutiny in terms of its behaviour under fire conditions since the role of Celotex RS5000 PIR insulation in the Grenfell tragedy in London in 2017. It has for many years been used in commercial roofing systems, wall insulation, cladding systems in many modern buildings, and as a component in structural insulated panels (SIPs).

The core materials of PIR are similar to those used in polyurethane (PUR), except that the proportion of methylene diphenyl diisocyanate (MDI) is higher and a polyester-derived polyol is used in the reaction instead of a polyether polyol. The resulting chemical structure is significantly different, forming isocyanurate groups that the polyols link together, giving it a complex polymeric structure.

This structure means that PIR was generally accepted as performing significantly better than PUR against fire, previously thought to have excellent fire behaviour from being tested to high standards, but the Grenfell tragedy brought much of this into question. Shortly after the fire on June 23, 2017, the police confirmed that small-scale fire tests had been carried out, and Detective Superintendent Fiona McCormack commented, "The insulation was more flammable than the cladding. Tests show the insulation samples combusted soon after the test started.".

For more information visit Grenfell Tower fire and Celotex RS5000 PIR insulation.

[edit] Polyethylene (PE)

Polyethylene is, technically a thermoset resin, which means that it uses two different reagents at a balanced ratio to form a chemical chain to make up the plastic. These reagents are isocyanate (MDI) and polyol. PU in foam form is denser and more elastic than other foams, making used in furniture aside aswell as commonly for pipe insulation. It has also been used as a cavity injection or spray product aswell as in board form as a component part of metal composite material panel systems. It was infamously used as a component part of the rainscreen cladding system which contributed to the tragic Grenfell tower block fire in 2017 in which 72 people died. See also Grenfell Tower articles.

The product used was ACM PE (Aluminium Composite Material Polyethylene) which was installed as cassettes, which caught fire and spread flames across the facade eventually igniting the insulation layer beneath. One year after the fire in 2018 the UK government banned the use of combustible materials in and on the external walls of new blocks of flats, hospitals, residential care premises and student accommodation over 18 metres in height. On 1 June 2022, further changes were introduced, which included an outright ban on the use of Metal Composite Material (MCM) / Metal composite panels (MCP) or ACMs with an unmodified polyethylene (PE) core on all new buildings at any height.

Polyethylene (PE) products can be manufactured with a number of different modifications to improve fire performance, such as the addition of fire retardants, vinyl acetate modification (PE-VA), ethyl vinyl acetate (EVA) copolymers as well as using a mineral filler added to the Polyethylene to dramatically improve fire performance. Although the amount of mineral filler added to such products can vary from 5-50%, the higher percentages produce a product which is labelled as FR, for fire resistant and one that continues to be used in cladding systems.

In the case of the Grenfell fire the product Reynobond PE ACM cladding was used and reported by the press as being a ‘cheaper, more flammable’ option, when compared to the Reynobond FR, product which has a more fire-retardant core (through the use of a mineral filler and other additives) whilst the Reynobond A2 is quoted by the manufacturer as having a non-combustible core, 'containing over 90% inorganic mineral material'.

The University of Queensland, Australia have studied and tested a number of different cladding systems, many of which contain variations on polyethylene products, the library lists some 80 plus tested products published in an online library, which is freely available at https://claddingmaterialslibrary.com/

[edit] Phenolic Foam (PF)

Phenolic foam insulation is one of the more clearly fire-resistant oil-based rigid insulations and has a closed-cell structure. It is often used in commercial and industrial buildings, as well as in applications where fire safety is a top priority. Phenolics are an industrial plastic with a number of applications, also used for electrical applications and sealants, and as a substitute for acrylic as it is cheaper to produce.

Phenolic foam insulation is made by combining phenol-formaldehyde resin, a blowing or foaming agent (usually but not exclusively hydrocarbons), and an acid catalyst. When hardener is added to the mix and rapidly stirred, the exothermic reaction of the resin, together with the action of the foaming agent, causes foaming of the resin and then a rapid setting of the foamed material to create the rigid cellular structure.

[edit] Urea Formaldehyde Foam Insulation (UFFI)

Urea formaldehyde (UF), also referred to as urea-methanal, is a thermosetting resin or polymer that is produced from urea and formaldehyde. Urea formaldehyde foam insulation, or UFFI, was developed in the 1950s. Using various blowing agents, this expanding foam product could be mixed on site and pumped into building cavities, benefiting from its hardwearing characteristics. It was later used extensively during the energy crisis of the 1970s in Europe, the UK, Canada, and America.

Through fears of off-gassing, it was banned in Canada in the 1980s and later in the US; it was never banned in Europe. Urea formaldehyde (UF) is considered a formaldehyde releaser, which means it releases or off-gases formaldehyde to varying degrees and concentrations over time. Formaldehyde, being a known human carcinogen, is normally a concern only at higher levels; it is one of the most well-known volatile organic compounds, or VOCs, but is present in many household products in small amounts, for example, naturally in all forms of timber.

As such, products containing high levels of urea formaldehyde, such as UFFI, paints, and other products, have been slowly phased out or reduced in many countries, while lower-content products such as adhesives are regulated by countries, such as the EU REACH programme. Some evidence still suggests, however, that when first installed, UFFI had the potential to release significant amounts of formaldehyde into the indoor air, resulting in acute adverse health effects, with levels dropping rapidly with time.

Today, urea-formaldehyde-associated products are still produced, sometimes referred to as injection foam, dry-resin foam, amino foam, aminoplast foam, tri-polymer foam, or dry-resin foam, and while they bear a relation, specific product research should be carried out. Today, there are also more readily available possibilities and tools to measure VOCs in internal environments, post-completion, as well as more rigorous manufacturer regulations, particularly those products associated with formaldehyde release.

Meanwhile, research and development of alternatives have also led to a number of formaldehyde-free or no-added formaldehyde (NAF) glue products becoming available as alternatives. In terms of types of rigid foam insulation products, there are a variety of alternatives and yet a wider variety of other insulation products on the market.

[edit] Other types of rigid cellular insulants

[edit] Cellulose rigid foam

Cellulose rigid foam is a new innovative material that uses cellulose nanocrystals (CNC), extracted from cellulose fibers and fibrils, through acid hydrolysis, mixed with wood pulp and polyvinyl alcohol, to bind the crystals and form a type of elastic foam.

[edit] Cementitious foam

Cementitious foam insulation is similar to aerated concrete products made from a mixture of cement, water, and foam agents. Cementitious foam (or silicate foam) insulation is made of magnesium oxide (extracted from seawater) plus calcium (from ceramic talc) and silicate. In its wet form, the material resembles shaving cream, and it is pumped at low pressures into the area to be insulated.

[edit] Cellular glass insulation

Cellular glass insulation is a rigid thermal insulation that has recycled glass and sand as base materials, supplemented by mineral substances and other natural materials. It is an inorganic insulation material that is composed of millions of completely sealed glass cells.

[edit] Soy foam insulation

Soy foam insulation is usually a PUR or PIR foam product, though one where between 50% and 80% of the chemical based foam is replaced with soy. It is therefore by some considered to have a lesser impact becase the soy is renewable, although it remains a petrochemical based product.

[edit] Rigid foam-related products

[edit] Insulated metal panels

Some rigid foam insulations are used as a core material in composite panels. These panels combine insulation with structural support, making them suitable for walls, roofs, and floors in various industries, including construction and transportation.

[edit] Metal composite panel systems (MCP / MCM)

Composite cladding panels are often metal covered with a foam inner core; this produces a rigid, hard-wearing, thin product suitable for external cladding.

[edit] Structural Insulated Panels (SIPs)

Composite panels with a core of rigid insulation, such as expanded polystyrene (EPS), extruded polystyrene (XPS) or rigid polyurethane foam sandwich and glued between two layers of oriented strand board (OSB) or sometimes plywood.

[edit] Vacuum Insulation Panels (VIPs)

VIPs consist of a rigid core enclosed within a vacuum-sealed, airtight envelope. They offer exceptionally high thermal resistance in a thin profile and are used in applications where space is limited but high insulation performance is required.