50mm Insulation Board

A 50mm insulation board is a rigid thermal insulation board used to slow heat transfer through a building. At 50mm thick, it sits in the “thin but effective” range, thick enough to make a real difference, but slim enough to fit where space is limited, such as internal walls or refurbishment projects.

What is a 50mm thick insulation board?

A 50mm thickness insulation board is a factory-made rigid panel that reduces heat loss by trapping still air or low-conductivity gas within the structure. The board holds its shape and can be tightly fixed against walls, floors, or roofs without leaving gaps. This is important because gaps reduce performance by allowing air movement and thermal bridging.

Different insulation materials use different internal structures – beads, closed cells, foam, or sealed cores – but they all work on the same principle: slowing heat transfer by conduction and convection.

A 50mm thick insulation board is often preferred to provide reliable thermal performance without altering the primary structural build-up.

What is 50mm thin insulation board used for?

A thin 50mm insulation board can be used in various ways, including:

• Internal wall lining, especially solid masonry walls.
• Between floor joists or beneath suspended timber floors.
• Pitched roofs between rafters where depth is limited.
• Flat roofs – 50mm alone rarely meet current Part L requirements, but it’s commonly used in refurbishment overlays or layered build-ups.

In refurbishment work, the 50mm thick insulation board is popular because it improves comfort without forcing major changes to doors, windows, or finishes.

Types of 50mm insulation board thickness

50mm boards commonly come in these materials:

EPS insulation (expanded polystyrene)

EPS contains sealed air pockets. These slow heat transfer, ensuring consistent thermal performance. It has low water absorption when correctly specified and installed, meaning its insulation value stays stable in controlled moisture conditions.

XPS insulation (extruded polystyrene)

XPS has higher compressive strength than many other insulation types due to its dense, closed-cell structure. This is why it performs well beneath floors and slabs. XPS cells do not readily absorb water, so the board is suited to moisture-prone conditions.

PIR Insulation (polyisocyanurate)

PIR has low thermal conductivity (lambda value). It offers higher thermal resistance per millimetre at 50mm compared to polystyrene and is commonly installed in walls and roofs.

Phenolic insulation foam board

Phenolic boards offer even higher thermal performance than PIR at the same thickness. They are used in tight spaces, especially where high thermal targets must be met with minimal thickness.

Kingspan Optim-R VIP (vacuum insulated panel)

VIP boards have a sealed vacuum core that restricts heat transfer. They give very high performance at 50mm. They must be ordered in precise sizes and handled carefully, as damage irreversibly compromises the vacuum and thermal performance.