The race toward Zero Carbon Ready Homes by 2025 makes insulation choice more critical than ever. With the latest Part L regulations raising performance requirements, designers and builders must select materials that deliver both efficiency and value for money.

That’s why we’ve broken down the most widely used thermal insulation boards—giving you a clear comparison so you can specify with confidence and match the right solution to your client’s brief.

Polyisocyanurate thermal insulation boards have a closed cell structure that can withstand external impacts and moisture and is a very popular choice for its effective and efficient thermal properties. PIR thermal insulation is rigid, durable and offers a compressive strength of 120-150 kPa. It’s a great thermal solution even when used as a thin board.

In mid-2021 the price of PIR insulation has seen an increase, which is largely due to the supply of raw materials required for manufacture. Currently in 2023 it stands at around £25-£30 per square metre.

• Low thermal conductivity of 0.021-0.028 W / (m * K).
• Compressive strength of 150-400 kPa.
• Moisture resistant with built in vapour barrier.
• Long life span of 50+ years.
• Fire resistant, burns but does not melt.

• Not classified as A1 or A2 Euroclass, banned for buildings above 11m.
• Performance can be compromised by exposure to moisture, or by damaged foil facing.
• Produces toxic smoke when next to fire, however, does not continue when fire is removed.
• Must be installed and handled with correct PPE to avoid irritations to the skin, eyes and respiratory system.

Rigid polyurethane (PUR) insulation is like PIR in the sense that they both are derived from polyurethane and has very similar thermal and material properties of PIR insulation, however the biggest difference is the difference in which PUR handles fire. PUR burns more and produces more smoke; however, the fire and smoke does not linger as the threat of fire is removed. However, it still has excellent thermal properties and is more economically viable for smaller projects.

The price of PUR insulation boards in 2023 is around £22-£26 per metre square not including installation.

• Low thermal conductivity of 0.021-0.028 W / (m * K).
• Compressive strength of 150-400 kPa.
• Vapour resistance by slowing down passage of vapour but does not completely stop it.
• Long life span of 50+ years. 25+ years for refrigerators.
• Fire resistant, burns (slightly more than PIR) and does not melt.

• Not classified as A1 or A2 Euroclass, banned for buildings above 11m.
• Performance can be compromised by exposure to moisture, or by damaged foil facing.
• Produces more toxic smoke than PIR when next to fire, however, does not continue when fire is removed.
• Must be installed and handled with correct PPE to avoid irritations to the skin, eyes and respiratory system.

Extruded polystyrene (XPS) insulation as the name suggests is manufactured through a process of extrusion, creating a smooth skin and closed-cell structure, making it ideal for thermal insulation in walls, ceilings and roofs not to mention it’s outstanding qualities for below ground applications.  It is essential a plastic material and will not rot or support growth of mould or mildew, as it provides no nutrient value to vermin.

In 2023 the price of XPS insulation boards is around £18-£22 per square metre, depending on the thickness, not including installation.

• Reasonable thermal conductivity of 0.033-0.035 W / (m * K).
• Compressive strength of 300-900 kPa
• At 1 inch it is vapour-semi-permeable, over 1.5+ inch XPS becomes a vapour barrier.
• A sustainable product, as the energy, resources and emissions saved greater outweighs the environmental impact it takes to produce them and will continue saving energy for decades.

• Fire classification is not great, with a Euroclass E rating. XPS is combustible and must be kept clear of any threat of fire. XPS softens at 165°F and melts between 200°F-210ºF which poses a risk of fire spread.
• R-value of XPS continually decreases over 50+ years.
• XPS manufactured with CFCs or HCFCs, hydrofluorocarbons are harmful to the ozone layer. XPS manufactured with HFC is free of chlorine and does not harm the ozone layer, however, is 1,430 times as potent a greenhouse gas as carbon dioxide.

Expanded polystyrene (EPS) insulation is manufactured by applying heat or steam to granules of foam within a mould, causing them to expand and form. Air is an excellent thermal insulator, and EPS is essentially 2% polystyrene and 98% air.

In 2023 the price of EPS insulation is £18-£22 per square metre, not including installation.

• Low thermal conductivity of 0.032 W / (m * K).
• Compressive strength of 70-250 kPa, EPS can be produced to meet specific strength requirement.
• Absorbs small amounts of moisture more compared with other rigid-foam insulations, however sheathing and facers EPS products are available to mitigate the vapour permeability. Unfaced 25mm (1 inch) thick EPS insulation ranges from 2.5-5.0 vapour permeability.
• Durable, rot proof and permanent material when specified and installed properly. It has an outstanding shelf-life of 100+ year cycle and will remain effective without loss of effective thermal conductivity.
• Is 100% recyclable and environmentally friendly, as no toxic substances are used in manufacturing EPS.

Glass wool is typically supplied in a roll or slab, and is made from natural sand, limestone and soda with a high proportion of recycled glass, plus other minerals. During manufacture these materials are melted at 1400-1500 °C and spun into cotton candy like fibres by forcing it through a fine mesh through centrifugal force, and then cooling with contact of air. Strength and cohesion is achieved through use of a binder that ‘cements’ the fibres together.

In 2023 the price of is quite cheap ranging from £5-£18 per metre square depending on thickness, and not including installation.

• A1 Euroclass. Completely fire retardant and can never contribute to a fire or emit any smoke or flaming droplets.
• Reasonable thermal conductivity of 0.035-0.044 W / (m * K). There is a claim that glass wool insulation can reach a thermal conductivity of 0.023 W / (m * K), however we are unable to find products with this specification.
• Vapour permeable and can reduce condensation within the building.
• 70+ long life span and should last a lifetime, however it can be easily damaged which will affect the thermal conductivity if the integrity is tarnished.
• Very environmentally friendly and sustainable, due to being a recycled material and being made from a highly abundant materials like sand.

• Compressive strength of only 11 pounds per square ich (psi), which means significant damage can be caused to insulation quite easily, however not as bad a mineral wool.
• Always wear PPE to avoid mechanical irritation to the eyes, skin and ensure no harmful airborne particles enter the respiratory tract.
• If not properly ventilated or the glass wool gets damp, then there is chance of promoting growth of fungi, mildew and rot, which dramatically reduces its thermal properties.

Mineral wool is typically produced from slag generated by iron and steel plants as a by-product of the blasting furnace, or by a mix of slag and rock. It is non-combustible and can resist temperatures above 1,000°C which is why it typically specified for external walls, roofs and upper floor insulation, as well as fire-resistant partition wall and doors.

• Either A1 or A2 Euroclass non-combustible.
• Reasonable thermal conductivity of 0.035-0.037 W / (m * K).
• 70+ long life span and should last a lifetime, however it can be easily damaged which will affect the thermal conductivity if the integrity is tarnished.
• Very environmentally friendly, as it can be recycled in many ways.
• Vapour permeable, so can be applied externally without trapping moisture in the wall.
• Its hydrophobic, and will although water can pass through, it won’t absorb water or develop mould or mildew.

• A high density 8 PCF mineral wool reaches 5% compression with only 0.42 pounds per inch (psi), which means significant damage can be caused to insulation quite easily.
• Always wear PPE to avoid mechanical irritation to the eyes, skin and ensure no harmful airborne particles enter the respiratory tract.