Mineral Wool Insulation vs Fiberglass 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.

Stone mineral wool costs roughly to per square metre at 100 mm against to for glass wool in 2026, a premium of 50 to 80 percent between two materials that insulate almost identically, both around 0.032 to 0.044 W/mK. Strictly speaking both are mineral wools, glass wool spun from recycled glass and stone wool from volcanic rock, and the price gap buys density rather than warmth.

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

That density is worth paying for in specific places: stone wool’s mass gives it markedly better acoustic performance, which is why party walls, floors between rooms and studios specify it; its fire behaviour is the best in mainstream insulation, non-combustible to the highest classification and used as fire-stopping in its own right; and it holds its shape in vertical and semi-exposed applications where lighter glass wool can slump. Across a loft floor, none of that earns its premium, and glass wool’s lightness even makes it easier to handle overhead, which is why lofts are yellow and party walls are green-brown. Handling has improved in both families, with modern low-itch bonded products a long way from the fibreglass of memory. The rule of thumb: horizontal and thermal, glass wool; vertical, acoustic or fire-critical, stone wool.

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.