85mm Insulation

85mm insulation is a mid-range to deep insulation thickness used in buildings where heat control needs to be reliable, not merely adequate. At this depth, insulation stabilises indoor temperature and helps the structure perform properly throughout the year. It is a thickness often specified when energy efficiency matters, but space must still be managed carefully.

What is 85mm Thick Insulation?

85mm insulation thickness means the material measures 85 millimetres from the warm side to the cold side once installed. That depth allows insulation to retain a sufficient volume of still air while fitting within common construction build-ups.

Most 85mm thick insulation comes as:

• Rigid boards (PIR, phenolic, EPS, or XPS). They hold their shape and give predictable performance.
• Mineral wool slabs. They are compressible and rely on thickness rather than rigidity.

85mm thickness insulation functions as part of a wider building system, influencing U-values and condensation risk when correctly detailed.

What is the Insulation 85mm Thickness Used For?

This thickness is commonly used where moderate-to-high thermal control is needed without overbuilding.

Typical uses include:

• Timber-frame walls with depths matching standard stud sizes.
• Internal wall upgrades, when improving heat retention, without rebuilding the structure.
• Floors over unheated spaces, such as garages and voids.
• Roof build-ups, especially between rafters, where space is limited.

Thick 85mm insulation offers dependable performance when there is no room for very deep layers.

Benefits of 85mm Insulation Thickness

The main advantage of this depth is balance. Other advantages of using 85mm insulation are:

• Strong thermal resistance without excessive wall or floor build-up.
• Better temperature stability, reducing hot-cold swings indoors.
• Improved compliance with UK Building Regulations when correctly specified.
• Material flexibility, since many insulation types are available at this depth.

FAQ

Where to buy 85mm insulation

You can buy 85mm insulation online directly from Insulation Wholesale. We stock a wide range of 85mm products, including mineral wool options. We supply UK-held stock, offer clear pricing, and support both trade and bulk orders. Our team will help you choose insulation that actually fits your build-up.

How to cut 85mm insulation

• Rigid boards: Score deeply with a sharp knife along a straight edge, then snap. For harder boards, a fine-tooth saw gives better control.
• Mineral wool slabs: Use a long serrated blade or an insulation saw. Cut a bit oversize so the slab friction-fits and holds itself in place.

A tight fit matters more at this thickness because gaps reduce performance.

How to fix 85mm insulation

Fixing is not only about holding insulation in place. It is also about maintaining the continuity of the thermal layer.

• Between studs or joists: Cut to friction-fit so the insulation stays in place without sagging.
• For solid surfaces: Use mechanical fixings designed for the insulation depth. Combine with adhesive for stability.
• Layered systems: Ensure boards are tightly butted, with staggered joints where possible, to limit heat paths.