Multifoil Insulation vs PIR Cost Calculator

How this calculator works

This calculator works in ranges rather than single figures, because real quotes, yields and tariffs genuinely vary that much. It starts from typical UK price, output and savings ranges drawn from published 2026 industry guides and official scheme documentation, then scales them by the quantities you enter and adjusts them for each choice you make below. The result is a low-to-high band that a realistic outcome is likely to fall within, not a promise of the figure you will achieve.

Multifoil quilt costs roughly to per square metre against to for 100 mm PIR in 2026, and at around 30 to 40 mm thick it is a fraction of PIR’s depth, which is precisely its pitch: reflective multi-layer blankets stapled and taped across rafters where space is tight. The comparison needs its asterisk stated plainly, because the two do not deliver equal performance per layer.

Area to insulate (square metres)

Enter the area to be covered in the material. Both options are priced per square metre for the same area so the totals compare directly; allow around 10 percent extra for cuts and waste when ordering boards, and check coverage per pack for rolls and quilts.

What else affects the figures

Multifoil works substantially by reflecting radiant heat, which requires unventilated air gaps either side to function, and its certified performance in proper build-ups is roughly equivalent to 50 to 70 mm of PIR rather than 100 mm, so like-for-like it is less insulation for less money and less depth, not a cheaper equal. Independent testing and certification is the ground to stand on: reputable multifoils carry BBA or LABC certificates specifying exact build-ups and the U-values they achieve, usually in combination with a layer of rigid or wool insulation rather than alone, and building control will ask for exactly that. Where multifoil genuinely earns its place is as the space-saving layer in hybrid build-ups, over-rafter in re-roofs, in conservatory ceilings and vans and outbuildings, and anywhere a continuous airtight radiant layer complements conventional insulation; as a sole substitute for the PIR your U-value calculation demands, it is the wrong tool honestly priced.

Certification, planning and grid connection

If a calculation here prompts a project, Building Regulations Approved Document L is the standard the work should meet, with U-value targets for each element, and installers registered with TrustMark or a competent person scheme can self-certify compliance. Check grant eligibility before paying for anything: ECO4 runs to 31 December 2026 and the Great British Insulation Scheme continues alongside it, both funding measures partly or fully for qualifying households, and domestic insulation carries 0 percent VAT until 31 March 2027 in any case. An EPC assessment before and after larger projects evidences the improvement for future buyers and lenders.