Insulation knife buying guide: edge, then length
Updated: October 2026
You have a loft roll on the landing, or foil-faced board still in the wrap, and amazon.co.uk has mixed a 550 mm wave saw with a short roofing knife. An insulation knife is the long hand blade for mineral wool, glass fibre or rigid foam, with less tearing than a wood saw. This page is the decision order only: edge, then a length you can check, then a sheath. The six-row table and the 19 October 2026 prices are in the [insulation knife comparison](/hub/cutting-tools/insulation-knife). Peter F. wrote this for DIY & tools. A qualifying purchase can earn a commission at no extra cost to you.
You have a loft roll on the landing, or foil-faced board still in the wrap, and amazon.co.uk has mixed a 550 mm wave saw with a short roofing knife.
You have a loft roll on the landing, or foil-faced board still in the wrap, and amazon.co.uk has mixed a 550 mm wave saw with a short roofing knife. An insulation knife is the long hand blade for mineral wool, glass fibre or rigid foam, with less tearing than a wood saw. This page is the decision order only: edge, then a length you can check, then a sheath. The six-row table and the 19 October 2026 prices are in the insulation knife comparison. Peter F. wrote this for DIY & tools. A qualifying purchase can earn a commission at no extra cost to you.
Our top picks
| Badge | Product | Blade style | Blade length | Guard | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  Everhard Everhard MK46000 insulation knife | Short fixed insulation knife | 3-5/8 in (bullets); overall 7.5 in | Sheath listed; reviews dispute it | 7.4 | about £19.01 | View offer |
| Best value |  Spear & Jackson Spear & Jackson B98INS Predator insulation saw | Insulation saw | 350 mm (14 in) on the listing | Reviews mention a guard that is awkward to fit | 8.4 | about £11.48 | View offer |
 Bahco Bahco PC-22-INS insulation saw | Waved insulation saw | 550 mm (22 in) | Not listed; reviews ask for one | 8.8 | about £15.92 | View offer |
On this page
Four blades, four jobs
This set is four tools wearing one search term. A wave-tooth saw, the Bahco PC-22-INS at £15.92, slices mineral wool and, in UK reviews, thinner PIR with less dust than a circular saw. A toothless carbon-steel curve, the Spear & Jackson B98INS Predator at £11.48, is the loft-roll blade. A serrated stainless saw, the Trade 4 You YHSC, is sold for XPS, PIR, polystyrene and wool, with a scabbard; the single is £11.95 and the two-pack is £18.50. The Everhard MK46000 at £19.01 is a short ISO knife. The folding Bahco 396-INS is a pocket wool saw.
Stars do not choose the family. The YHSC pair shows 5.0 from six shared ratings. The Everhard shows 4.7 from 371, but the texts are from the United States. The Bahco wave saw is 4.1 from 540. Glass wool or stone wool starts with toothless or wave. Foil-faced PIR under about 50 mm is usually a serrated saw or a score-and-snap. Named picks sit on the best insulation knife page.
Length you can check
Thickness first, then millimetres you can actually read. The Bahco PC-22-INS is 550 mm (22 in). UK retail copy on Wickes and PrimeTools allows EPS and XPS up to 75 mm on that saw. It does not promise 100 mm Kingspan.
The Predator is the conflict you must not average. The amazon.co.uk listing says 350 mm (14 in). Spear & Jackson’s own page states a 270 mm toothless blade and 442 mm overall. The Centre for Sustainable Energy describes 270 mm as the usual mineral-wool loft depth, which is a loft figure, not a knife specification.
The Everhard bullets say 3-5/8 in. A separate attribute says 8 inches and retractable, which clashes with the fixed knife, so the bullet length is the one to use. The folding 396-INS is sold in UK shops around 185–190 mm. The Amazon block claims 12 inches and 100 volts. That 12 in figure is unusable. Entry in this scrape is about £11–£12. Mid is about £16–£20, on 19 October 2026.
Sheath and who can buy it
A 190 mm or 550 mm blade is not the 3-inch folding pocketknife exception. In England and Wales, section 141A of the Criminal Justice Act 1988 makes it an offence to sell a knife to someone under 18, with that short non-locking exception. A loft job at home is not a reason to take the saw on the bus.
The Bahco PC-22-INS listing does not put a guard in the included-components line. Wickes mentions a rust sleeve; that is a shop page, not this amazon.co.uk box. The Predator reviews mention an awkward guard. The YHSC listings name a scabbard. The Everhard line says sheath; the US texts say cardboard or nothing. The folding 396-INS has no sheath named in the listing fields. Put the cover on before you climb the loft ladder.
What this page will not rank
If the material is glass wool or stone wool, start with a toothless or wave blade whose length you can check. If it is foil-faced PIR under about 50 mm, use a serrated saw or a score-and-snap. If the listing is 5.0 from six shared YHSC texts, or a field says 7 RPM, 4500 RPM or 100 volts, drop that field. Once the edge, the length and the sheath are named, buy that one listing.
Common questions
Is an insulation knife the same as a wood saw?
No. A wood saw has teeth meant for timber and throws more fibre from a quilt. An insulation knife is a wave, toothless, serrated or short roofing blade sold for wool or foam. ROCKWOOL prefers a knife, with extraction if you switch to a power tool.
What blade length do I need for a loft roll?
You need a blade that can cross the batt in one pass without a 90 mm trimmer. The Bahco PC-22-INS is 550 mm. The Predator listing says 350 mm; the maker says 270 mm. The Centre for Sustainable Energy describes 270 mm as the usual mineral-wool loft depth, which is a loft figure, not a knife spec. The Everhard’s 3-5/8 in blade is a roofing trimmer.
Will a 550 mm wave saw cut 100 mm PIR?
Not as a promise. Wickes and PrimeTools cap EPS and XPS at 75 mm on the Bahco PC-22-INS. UK reviews of that saw are often clean around 50–70 mm and mixed at 90–150 mm, where the thin blade binds or wanders. Keep a fine-tooth wood saw for the long square cut in thick foil board.
Can a shop sell this to someone under 18?
Not in England and Wales, except for a folding, non-locking pocketknife with a cutting edge of three inches or less. These insulation blades sit outside that exception. GOV.UK also requires a good reason to carry a knife in public. A loft job at home is not a reason to take the saw on public transport.
Are pipe-lagging plastic guides the same tool?
No. A split plastic jig that slides along a pipe is for lagging, not for a loft roll or a sheet of Kingspan. Those guides, wire strippers, 150 mm HVAC knives and multi-tool blades were removed from this comparison. If the listing does not show a long hand blade for wool or board, it is a different product.
Related pages
Sources
Public UK sources from the research digest. Listing prices, stars and review counts are the amazon.co.uk lines used for this comparison, checked on 19 October 2026.
- GOV.UK — Buying and carrying knives (retrieved 19 October 2026)
- Criminal Justice Act 1988, section 141A (retrieved 19 October 2026)
- ROCKWOOL UK mineral wool safety data sheet (retrieved 19 October 2026)
- FEF mineral wool health and safety factsheet (retrieved 19 October 2026)
- PrimeTools — Bahco PC-22-INS insulation saw (retrieved 19 October 2026)
- Spear & Jackson — Predator insulation saw B98INS (retrieved 19 October 2026)
- Centre for Sustainable Energy — loft insulation (retrieved 19 October 2026)
- GOV.UK — Approved Document L 2026 (retrieved 19 October 2026)