25mm Insulation Board

The 25mm insulation board is a rigid insulation board installed to slow heat transfer within a building’s fabric, improving thermal performance and indoor temperature stability.

This insulation thickness is used to add thermal resistance in places where thick insulation cannot fit.

What is 25mm Thick Insulation Board?

25mm insulation board thickness means the board is exactly 25mm thick. The core material is designed to restrict air movement or use closed-cell structures to reduce heat transfer –still air has lower thermal conductivity than dense materials such as timber or masonry.

Even though it is relatively thin, a thin 25mm insulation board can make a noticeable difference in energy use when added to a build-up of other insulation layers.

The 25mm insulation thickness is available in different materials, which gives each type varying thermal resistance, compressive strength, and moisture performance.

What is 25mm Insulation Thickness Board Used For?

A 25mm insulation board is mainly used:

• Behind internal linings where thicker layers will not fit.
• Inside stud walls before plasterboard is fixed.
• Beneath floor finishes or screeds, where a small increase in overall U-value contributes toward compliance without fitting the floor too high.
• In partitions or ceilings to improve thermal or acoustic comfort.

Because it is thin, it’s not usually the main insulation for a roof or external wall. It improves the performance of the overall insulation build-up.

Types of 25mm Insulation Board

25mm boards mainly come in these materials:

EPS insulation Board

EPS boards’ closed-cell structure traps air and slows heat flow through the material. This minimises heat gain or loss.

The lightweight foam material is easy to cut and has good moisture resistance, but should still be detailed to prevent prolonged water exposure.

EPS boards are commonly used in floors and some cavity wall applications, and as backing insulation in external wall insulation systems.

Phenolic insulation Board

Phenolic boards use a special polymer foam that gives a lower thermal conductivity per millimetre than many other boards.

They are lightweight and have a relatively low thermal conductivity – a 25mm thick insulation board of phenolic foam delivers better insulating effect than many same-thickness alternatives.

PIR Insulation Board

PIR boards combine a rigid foam core with foil facings to deliver excellent thermal efficiency.

A 25mm PIR board offers a good balance of heat resistance, strength, and build quality. PIR boards 25mm are widely used in walls, roofs, and floors where higher performance is required in limited spaces.

Kingspan Optim-R VIP Board

VIP boards are a high-performance, advanced option used where you need the best thermal resistance in the smallest thickness.

They contain a core sealed under vacuum, which almost eliminates air and reduces heat transfer far more than foam boards. This makes an ultra-thin board like VIP extremely high thermal insulation in areas with severe space restrictions.

However, VIPs are more expensive and must be handled carefully – cutting them on site or damaging the vacuum leads to performance loss.

Benefits of Thin 25mm Insulation Thickness Board

Here are some advantages of using a thin 25mm insulation board:

• Space efficient – It fits where thicker boards would push finishes out too far.
• Improves the overall thermal performance of layer build-ups – When layered with other insulation types, it boosts total thermal performance without adding bulk.
• Easy to handle – Lightweight and easy to cut accurately.
• Versatile – Works in walls, floors, ceilings, and partitions where small gains in insulation matter.
• Cost-effective – The cost per square metre is competitive for thin upgrades – especially in EPS and PIR – when extra thickness is not an option.

FAQ

Where to buy a 25mm insulation board?

You can buy an insulation board 25mm thick online from Insulation Wholesale, a leading UK supplier that stocks a wide range of insulation materials, including EPS, PIR, phenolic, and VIP in 25mm thin insulation board sizes. We work directly with leading brands to offer UK stock at competitive pricing, with fast nationwide delivery to your site.

How to fix 25mm insulation board?

Correct installation of 25mm thick insulation board ensures it performs well:

• Measure and cut the insulation to a size that suits the space. Use a sharp insulation knife and a straightedge.
• Clean all dust and loose debris from the surface. Use fixings compatible with both the insulation type and the substrate:

1. On walls, use a suitable insulation adhesive or masonry fixings to hold the boards plumb.
2. On floors or ceilings, use mechanical fixings like insulation retainers or screws with washers.

• Butt the boards tightly edge-to-edge and seal gaps with foil tape or compatible sealant. This helps reduce thermal bridging.
• Confirm alignment before installing plasterboard or finish. A flush surface makes decoration and lining easier.

Follow manufacturer guidance for the specific type of board you are installing.

Where to install 25mm insulation board?

A 25mm insulation thickness board is best where space is limited, but some performance gain helps. Install it:

• Behind internal lining in stud or retrofit walls.
• In ceilings or loft hatch surrounds where high insulation has been fitted elsewhere, and you need a finishing layer.
• Around service runs or reveals to reduce cold spots.
• Inside partition walls where thermal comfort matters.

25mm is rarely the sole insulation layer in large roofs or thick walls, but it complements thicker layers effectively.