20mm Insulation Board

The 20mm insulation board is a very thin, rigid insulation material used in new-build and refurbishment projects to improve thermal performance where build-up space is tight. It is also used where only a small depth is needed for retrofit or internal finishing.

20mm boards are rigid but lightweight, designed to sit inside walls, floors, or roofs to reduce heat transfer through these elements.

What is 20mm Insulation Thickness Board?

A 20mm insulation thickness board is a solid panel made from foam or a specialised insulating material. That dimension is much thinner than most boards used on site – most boards are typically 50–100mm + thick. However, it still provides measurable thermal resistance when installed correctly.

A key determinant of its performance is the material inside. Some materials rely on closed-cell foam structures, while others use advanced core technologies. A 20mm board’s thermal conductivity (how easily heat travels through it) tells you how well it insulates.

Typical PIR 20mm boards have a lambda value of 0.022–0.026 W/m·K; EPS 20mm typically has a lambda value of around 0.030–0.038 W/m·K. Lower values indicate improved insulation.

20mm rigid insulation comes in standard panel sizes – often 2400mm x 1200mm – that can be cut to fit studded walls, ceilings, or floors.

What is 20mm Insulation Board Used For?

A thin 20mm insulating board is appropriate for:

• Internal stud walls or partitions where every millimetre counts before finishing.
• Between roof rafters, where loft insulation is being upgraded, and space is restricted.
• Retrofit applications where you must improve insulation on an existing build without major structural alterations.

It is often used as part of a multi-layer system in walls or floors to reinforce thermal performance.

This thickness will not meet full building regulations on its own in new builds, but it can be part of a layered build‑up to help reach required U-values.

Types of 20mm Thick Insulation Board

Thin 20mm insulation is available in the form of:

PIR Insulation (Polyisocyanurate) Boards

PIR boards are rigid foam panels that often come with aluminium foil facings. They perform efficiently for their thickness, meaning they offer more insulation per millimetre than basic foam products. They are also generally stable and easy to handle. Many UK brands offer 20mm PIR boards for wall, floor, and roof systems.

• Good thermal resistance for the shallow depth.
• Lightweight and cuttable with sharp knives or saws.
• Commonly specified in modern wall, floor, and roof build-ups.

EPS Insulation (Expanded Polystyrene) Boards

EPS boards are made from tiny polystyrene beads expanded together. They are cost‑effective and useful where high thermal performance is not the primary requirement. Their insulation value per thickness is lower than PIR’s, but they are still workable and commonly available.

• Easy to cut, but edges can crumble.
• Good for basic insulation and fixing under screeds.

Kingspan Optim-R (Vacuum Insulation Panels)

VIP boards use a sealed vacuum around a special core to dramatically increase thermal resistance compared with PIR or EPS – much higher performance in the same 20mm depth.

This is great in tight areas, but you must not cut, drill, or puncture them on site because that destroys the vacuum and the insulation performance.

• Very low heat transfer rate – very efficient.
• Expensive and more fragile than traditional panels.
• Mostly used where space and high performance are critical.

VIP panels are usually covered with protective facings to reduce on-site damage. They are normally fragile and should be handled carefully.

FAQ

Where to buy a 20mm insulation board?

You can get 20mm insulation boards online at Insulation Wholesale. We sell PIR and other board types at competitive wholesale pricing, with trade discounts and pallet deals for larger orders. Our team can help you pick the right board for the job. UK stock available for fast nationwide delivery.

Can you cut a 20mm insulation board?

Yes. You can cut PIR and EPS insulation using either of these:

• A sharp utility knife
• Insulation saw
• Powered saw with a fine blade

You need to cut the board to fit around beams, joists, and irregular spaces.

However, you should not cut VIP (vacuum insulation panels). That will break the airtight vacuum that makes these panels effective. Once that vacuum is lost, insulation performance drops dramatically.

Wear appropriate PPE and control dust in line with site health and safety requirements.

How to fix 20mm insulation board?

Here’s how you typically fix a thin 20mm insulation board:

• Apply suitable construction adhesive or the dot-and-dab method to flat surfaces (e.g., dot and dab to ceilings and walls).
• Mechanical fixings (special insulation screws or fixings) where adhesives will not do.
• Between timber battens and joists – Cut the board to fit snugly between timber battens or joists so it is held mechanically.

Make sure edges are well sealed to limit draughts, and follow the manufacturer’s instructions if the panel has foil facings or vapour control layers.