Glass Fiber vs Mineral Wool Insulation 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.

Glass fibre costs roughly to per square metre at 100 mm against to for stone mineral wool in 2026, making it the cheapest mainstream insulation in Britain, and since both materials insulate at essentially the same 0.032 to 0.044 W/mK, glass wool delivers the most warmth per pound of anything on the merchant’s shelf. Both are technically mineral wools, one spun from recycled glass and one from volcanic rock, cousins separated mainly by density.

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

Buying from the glass wool side, the question is what would justify paying more for stone: the answers are sound, fire and structure. Stone wool’s extra mass absorbs noise dramatically better, its non-combustibility grades higher and it doubles as fire-stopping, and its stiffness holds vertical friction-fits where lightweight glass rolls slump, which maps to party walls, floors, studs and anything acoustic or fire-rated. If the job is a loft floor or any horizontal thermal fill, nothing about stone wool improves the outcome and glass wool’s lightness actually handles better overhead, so bank the difference. Modern glass wool from Knauf, Isover and URSA is bonded, low-itch and a world away from its reputation, though gloves and a mask remain sensible with either family. Same logic, opposite starting point, as our mineral wool versus fiberglass page above.

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.