Topping up a glass-wool loft
You want less tearing than a wood saw on a quilt or a rock-wool slab, plus a mask. The Predator is the toothless saw praised on fibre rolls. Take short strokes, and do not expect it to like thick foil board.
Insulation knife comparison 2026
The best insulation knives, compared.
Top pick: Trade 4 You insulation saw Best value: Spear & Jackson B98INS Predator insulation saw – Score 84 at about £11.48, the usable fibre saw after the top pick is assigned, with 4.2 from 122 reviews. Updated October 2026.
Charlie White (Charlie DIYte)Expert source
An insulation knife is a long hand blade for slicing mineral wool, glass wool or rigid foam board. A wood handsaw tears the quilt and throws more dust. Judge it by a sheath, a blade length you can check, and an edge you can resharpen. Reviewers like cuts around 50 mm and describe binding or wandering on 90–150 mm. The [insulation knife buying guide](/hub/cutting-tools/insulation-knife/sub/insulation-knife-buying-guide) sets the order: material, then a length you can verify, then the edge. On amazon.co.uk it also appears as an insulation saw, a toothless blade, a short roofing knife or a folding wool saw. Pipe-lagging jigs, wire strippers, duct knives and multi-tool blades are a different product and are not in the table.
An insulation knife is a long hand blade for slicing mineral wool, glass wool or rigid foam board. A wood handsaw tears the quilt and throws more dust.
22 products checked · 54 hrs invested · +18,400 readers
6 of 6: Best insulation knives compared
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1-2 of 6Best overall
Best value
5.8/10
5.6/10
7.4/10
8.4/10
8.8/10
6.8/10
∼ £12
∼ £19
∼ £19
∼ £11
∼ £16
∼ £20
5.0(6)
5.0(6)
4.7(371)
4.2(122)
4.1(540)
4.0(15)
Personal buying guide
Which insulation knife fits the job?
Question 1 of 2
What are you cutting?
The best insulation knives in detail
Our view
The Trade 4 You YHSC is a serrated stainless insulation saw at about £11.95, listed at 200 g, with a scabbard in the included-components line. The amazon.co.uk line is 5.0 from 6 reviews. The four written reviews are the same texts as on the two-pack ASIN, and one of them describes a three-pack, so the sample is not a test of this single saw. The short praise is less mess than a handsaw or jigsaw on Kingspan or Celotex-type board, from a buyer who had only tested the tool. One complaint is a sharp blade left on the doorstep without a signature. Blade length is not a verified millimetre figure in the usable fields; the listing gives a 43 cm package size. Do not treat the 5.0 as a ranking in this comparison. The editorial score is 58. That is not a lab result.
Pros
- Scabbard listed
- Serrated stainless blade claimed for PIR, XPS and wool
- about £11.95
Cons
- 5.0 from only 6 ratings, shared with the two-pack
- One review text is about a three-pack
- Blade length not verified beyond package size
Best for: You want a sheathed serrated saw and will treat six shared ratings as a thin sample.
Less suitable: Anyone ranking from stars, or a loft job that needs a 550 mm wave saw with hundreds of reviews.
Specifications
- Model
- Trade 4 You insulation saw
- Brand
- Trade 4 You
- Price
- ∼£12
- Customer rating
- 5.0/5(6)
- Blade style
- Serrated saw
- Edge
- Serrated
- Guard
- Yes
- Folds
- No
- Weight
- 200 g
- Blade material
- Stainless steel
- Pack
- Single
- Handle
- Ergonomic
Common questions
Is this the same saw as the two-pack?
The model number is YHSC on both ASINs. This listing is one item at 200 g and about £11.95. The two-pack is a different ASIN at 420 g and about £18.50.
How many reviews does the 5.0 rest on?
The listing line is 5.0 from 6. The four written reviews are the same texts as on the two-pack, and one of them describes a three-pack.
Does it come with a sheath?
Included components say scabbard. A shared review describes a rigid sheath with Velcro, in a text about a three-pack.
Our view
The Trade 4 You two-pack puts two YHSC serrated saws in one listing at about £18.50, with a listed weight of 420 g against 200 g on the single. The amazon.co.uk line is the same 5.0 from 6 as the single ASIN, and the four written reviews match word for word. One of those texts talks about three saws, which does not match a two-pack title. The shared praise is a cleaner PIR offcut than a traditional saw, plus a rigid sheath with Velcro in the three-pack write-up. Unsigned delivery of a sharp blade is the shared complaint. There is no separate defect note for this pack. Treat it as two of the same thin-sample saw, not as a second test. The editorial score is 56. That is not a lab result.
Pros
- Two serrated saws, scabbard listed
- Claimed for loft insulation, PIR and XPS
- about £18.50 for the pair
Cons
- Same six ratings as the single ASIN
- A shared review describes a three-pack
- No separate defect notes
Best for: You already accept the YHSC as a thin-sample serrated saw and want a spare in the same box.
Less suitable: Anyone treating 5.0 from six shared ratings as a winner, or a job that needs a verified 550 mm wave saw.
Specifications
- Model
- Trade 4 You insulation saw, 2 pack
- Brand
- Trade 4 You
- Price
- ∼£19
- Customer rating
- 5.0/5(6)
- Blade style
- Serrated saw
- Edge
- Serrated
- Guard
- Yes
- Folds
- No
- Weight
- 420 g
- Blade material
- Stainless steel
- Pack
- 2-pack
- Handle
- Two-part
Common questions
How many saws are in the box?
The listing says 2 items and 2 packs. A review text shared with the single ASIN talks about three saws.
Are the reviews only for this two-pack?
No. The star line and the four written reviews match the single YHSC listing.
What handle does the title claim?
The title says an ergonomic two-component handle. The attribute block only says ergonomic handle.
Our view
The Everhard MK46000 is a short fixed insulation knife at about £19.01, 49.8 g, with a 3-5/8 in blade and 7.5 in overall length in the title and bullets. The amazon.co.uk line is 4.7 from 371 reviews. The written reviews are marked as reviewed in the United States, so they are not UK opinion; they describe roofing polyiso and about 2 in foil-faced foam, plus one attic-batt job against a straight edge. Included components say sheath; several of those US texts say there is no sheath, or only cardboard. A double-edged blade stops you pressing on the spine, and a thick blade binds in hard foam. Reviewers file the edge through a day of roofing cuts. This is a trimmer for ISO board, not a 550 mm loft saw. The editorial score is 74. That is not a lab result.
Pros
- 3-5/8 in high-carbon spring-steel blade in the bullets
- 49.8 g, overall 7.5 in
- 4.7 from 371 on the amazon.co.uk star line
Cons
- Review texts are from the United States
- Sheath listed; US texts dispute it
- Too short for a loft roll; double edge stops a spine push
Best for: Trimming roofing ISO board if you accept United States review texts behind a UK star line.
Less suitable: Glass-wool loft rolls, 100 mm PIR, and anyone who needs a sheath confirmed in UK reviews.
Specifications
- Model
- Everhard MK46000 insulation knife
- Brand
- Everhard
- Price
- ∼£19
- Customer rating
- 4.7/5(371)
- Blade style
- Roofing knife
- Blade length
- 92 mm
- Edge
- Double edge
- Guard
- Disputed
- Folds
- No
- Weight
- 49.8 g
- Blade material
- Spring steel
- Pack
- Single
- Handle
- Plastic
Common questions
How long is the MK46000 blade?
The title and bullets say 3-5/8 in, about 92 mm, and overall length 7.5 in. A separate attribute says 8 inches and retractable. Those clash with the fixed knife in the title, so the bullet length is the one shown.
Does it include a sheath?
Included components say sheath. Review texts, which are from the United States, say there is no sheath or only cardboard.
Are the written reviews from the UK?
The 4.7 from 371 is the amazon.co.uk listing line. The written reviews are marked as reviewed in the United States.
Our view
The Spear & Jackson B98INS Predator at about £11.48 is a 349 g carbon-steel insulation saw. Across 122 amazon.co.uk reviews the line is 4.2. UK buyers cut glass-fibre loft roll and rock wool with less tearing and less fibre cloud than a toothed saw, and they prefer it to a kitchen knife on a roll. 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, so those figures stay as a conflict. The blade wanders on long strokes, foil facing blunts it quickly, one review calls it useless on Kingspan, and it sticks in fire batt. Reviewers mention a safety guard that is awkward to take on and off, and they sharpen after a day on rock wool or foil. In this set it is the best value when the job is fibre, not thick foil-faced board. The editorial score is 84. That is not a lab result.
Pros
- about £11.48, 4.2 from 122 amazon.co.uk reviews
- Less fibre cloud on loft roll and rock wool than a toothed saw
- Sharp on arrival
- Reviewers mention a guard, even if it is awkward
Cons
- Listing 350 mm versus maker 270 mm
- Wandering on long strokes; foil and Kingspan complaints
- Needs sharpening after a day on rock wool or foil
Best for: Glass-wool loft roll and rock wool if you will take short strokes.
Less suitable: Thick foil-faced PIR, fire batt, and anyone who needs a verified 550 mm blade.
Specifications
- Model
- Spear & Jackson B98INS Predator insulation saw
- Brand
- Spear & Jackson
- Price
- ∼£11
- Customer rating
- 4.2/5(122)
- Blade style
- Toothless saw
- Blade length
- 350 mm listed
- Edge
- Toothless
- Guard
- Yes
- Folds
- No
- Weight
- 349 g
- Blade material
- Carbon steel
- Pack
- Single
- Handle
- Plastic
Common questions
Does the B98INS have saw teeth?
The attribute block says 5 teeth and 4500 RPM. Those clash with a hand-powered saw. UK reviews describe a toothless edge that slices rather than saws.
What insulation do the UK reviews praise?
Glass-fibre loft roll and rock wool, with less fibre cloud than a toothed saw. Foil-faced board and fire batt draw the complaints.
Is a guard included?
Included components do not list a guard. Reviewers refer to a safety guard that is awkward to take on and off.
Our view
The Bahco PC-22-INS is a 550 mm waved insulation saw at about £15.92, listed at 400 g, for mineral wool, stone wool and eco wool. Across 540 amazon.co.uk reviews the line is 4.1. UK buyers often finish 50 mm Kingspan and mineral-wool slabs with a clean edge and far less dust than a wood saw or circular saw, and they use it for angled cuts in board. At 90 mm, 100 mm and 150 mm PIR the same thin blade binds, flexes, or wanders off a long straight line, and full-length cuts in 60–75 mm board are described as hard work. Reviewers sharpen often; one bought a separate Bahco sharpener because the metal does not hold an edge. Several texts say there is no blade guard and compare it to a long bread knife. One replacement story mentions a smashed handle on arrival. In this set it is the top pick for a long wave saw with a large UK review set. The editorial score is 88. That is not a lab result.
Pros
- 550 mm waved blade, listed 400 g
- Less dust than a wood saw on wool and thinner PIR, in UK reviews
- 4.1 from 540 amazon.co.uk reviews
- Useful for angled cuts in board
Cons
- Binds or wanders on 90–150 mm PIR
- No blade guard in reviews that asked for one
- Needs frequent sharpening
Best for: Mineral-wool slabs and PIR around 50–70 mm when you want a long wave saw.
Less suitable: Long square cuts in 100 mm foil-faced PIR, and anyone who needs a sheath in the box.
Specifications
- Model
- Bahco PC-22-INS insulation saw
- Brand
- Bahco
- Price
- ∼£16
- Customer rating
- 4.1/5(540)
- Blade style
- Wave saw
- Blade length
- 550 mm
- Edge
- Wave tooth
- Guard
- No
- Folds
- No
- Weight
- 400 g
- Blade material
- Bi-metal
- Pack
- Single
- Handle
- Rubber
Common questions
How long is the Bahco PC-22-INS blade?
The listing’s included-components line says 550 mm (22 in). The same page also shows 7 RPM and a band-saw note, which do not match a hand saw.
Does the listing include a blade guard?
A guard is not in the included-components line. Several UK reviews say there is no guard and compare the blade to a long bread knife.
What do the reviews say about thick PIR?
In the texts read, cuts around 50–70 mm are often described as clean and low-dust. Cuts at 90–150 mm are often described as binding, flexing, or hard work.
Our view
The Bahco 396-INS is a folding insulation saw at about £19.99, listed at 200 g, with a highlight for glass and stone wool. Across 15 amazon.co.uk reviews the line is 4.0, and only two written reviews are available. One UK review cut 75 mm rock wool without the ripping of a utility knife. The other cut 140 mm recycled wood-fibre batts, called the blade just long enough, and sharpened before every cut. The attribute block says AC and 100 volts, and the blade-length field says 12 inches, which clash with a small folding hand saw, so those fields are not treated as specs. UK retail length for this saw is about 185–190 mm, which is the figure in the table. No sheath is named in the listing fields. Thirteen of the 15 ratings have no text here, so this is a pocket wool saw with a thin review set, not a loft-roll replacement for the 550 mm Bahco. The editorial score is 68. That is not a lab result.
Pros
- Folds for a bag
- Highlight names glass and stone wool
- One UK review cut 75 mm rock wool without a utility-knife tear
Cons
- 4.0 from 15, with only two texts
- Listing 100 V and 12 in fields conflict with a hand saw
- Needs a sharpen before every cut in the wood-fibre review
Best for: A short rock-wool batt you can fold a saw around, if you accept two written reviews.
Less suitable: A full loft roll, thick PIR, or anyone who needs a 550 mm blade and a sheath.
Specifications
- Model
- Bahco 396-INS folding insulation saw
- Brand
- Bahco
- Price
- ∼£20
- Customer rating
- 4.0/5(15)
- Blade style
- Folding saw
- Blade length
- 185–190 mm
- Folds
- Yes
- Weight
- 200 g
- Blade material
- Carbon steel
- Pack
- Single
- Handle
- Metal
Common questions
Is the 396-INS electric?
No. The title is a folding insulation saw. The attribute block says AC and 100 volts, which conflicts with that title, so those fields are not shown as specs.
What did the two written reviews cut?
One UK review cut 75 mm rock wool. The other cut 140 mm recycled wood-fibre batts and sharpened before every cut. Thirteen of the 15 ratings have no text.
Why is the Amazon 12 in length not used?
The listing blade-length field says 12 inches and the package size is 32 x 11 x 37 cm. Those clash with a small folding saw. UK retail length is about 185–190 mm.
How we compared
Six amazon.co.uk insulation-knife listings were scored for this page. Stars, review counts and shelf prices are the listing lines from 19 October 2026. There was no laboratory cut test. The four weights below sum to 100. A thin review sample, a shared review set, a hand-tool listing that quotes RPM or volts, review texts from another Amazon marketplace, an unverified length, and a 5.0 treated as a ranking all reduce the score.
1
Stars and review volume
40%About 40 points. The amazon.co.uk star rating and the review count both count. A handful of ratings loses weight against a file of several hundred.
2
Job fit and blade length
25%About 25 points. A wave or toothless edge for wool, a serrated edge for foil board, and a short roofing knife for ISO trim. The length has to be one you can check against the thickness you cut.
3
Review sentiment
20%About 20 points. Dust compared with a wood saw, a blade that wanders, foil that dulls the edge, and a missing guard all come from the written reviews.
4
Price
15%About 15 points. Shelf price in GBP on the amazon.co.uk listing, for a tool you can actually use on the job you named.
Independent review
Last updated: October 2026
8 sources checked
Insulation knife buying guide
Pick the material and the thickness first. A toothless or wave blade suits glass-wool rolls and rock-wool slabs. A serrated saw or a score-and-snap suits thinner foil-faced PIR. A 3-5/8 in roofing knife trims ISO board and will not cross a loft roll. Then check a length you can verify, a sheath on a long blade, and whether the reviews are actually about that listing.
What is an insulation knife?
An insulation knife is a long hand blade for slicing mineral wool, glass wool or rigid foam board with less tearing and less dust than a wood handsaw. On amazon.co.uk it also appears as an insulation saw, a toothless blade, a short roofing knife or a folding wool saw. The six tools in this comparison sit between about £11 and £20. Pipe-lagging jigs, wire strippers, duct knives and multi-tool blades are a different product and are not in the table.
Best for
- A householder topping up glass-wool loft roll, with a mask and a sheath
- Someone cutting a few sheets of PIR around 50 mm with a straight edge
- A roofer trimming ISO board with a short fixed knife
Not ideal for
- Unknown material that might be asbestos
- A fire-stopping batt, or a warm roof that must keep a continuous insulation line
- Pipe-lagging jigs, duct knives and multi-tool blades
Mistakes to avoid
- 1
Trusting RPM or volts on a hand saw
The Predator attribute block quotes 4500 RPM, and the folding Bahco quotes 100 volts. Both clash with a hand tool. Ignore those fields, and ignore a tooth count that contradicts a toothless edge in the reviews.
- 2
Long strokes on a thin blade
UK reviews of the Predator and the long Bahco describe wandering, flexing or binding when the stroke is long, especially in thicker PIR. Short strokes and a straight edge matter more than a star score.
- 3
A 5.0 from six shared ratings
The two Trade 4 You YHSC listings share the same 5.0 from 6, and one written review describes a three-pack. That is not a second test and it is not a ranking.
What to weigh up
Material and thickness
HighGlass-wool rolls and rock-wool slabs suit a toothless or wave blade. The Predator is the toothless carbon-steel saw in this set, at about £11.48 and 349 g. UK reviews praise glass-fibre loft roll and rock wool, with less fibre cloud than a toothed saw, and they complain about foil facing, Kingspan and fire batt. The Bahco PC-22-INS is the 550 mm wave saw. UK buyers often finish 50 mm board with less dust than a wood saw.
Blade length you can verify
HighBahco’s catalogue length for the PC-22-INS is 550 mm, and the listing’s included-components line agrees. That is the length in the table. Spear & Jackson states a 270 mm blade and 442 mm overall for the B98INS. The amazon.co.uk listing says 350 mm (14 in), so the table shows the listing figure and the conflict stays in the product notes. The Everhard bullets say a 3-5/8 in blade, about 92 mm, and 7.5 in overall.
Which option suits you?
Three typical situations, each with a recommendation from this comparison.
A few sheets of 50 mm PIR
Foil-faced board around 50–70 mm is the Bahco PC-22-INS job in the UK reviews: a long wave saw, less dust than a circular saw, and mixed results once the sheet gets toward 100 mm.
Trimming roofing ISO board
The Everhard MK46000 is a 3-5/8 in roofing knife, not a loft saw. The 4.7 from 371 is the amazon.co.uk star line. The written reviews behind it are from the United States.
Common questions about insulation knives
Which insulation knife is the top pick in this comparison?
The Bahco PC-22-INS at about £15.92. It scores 88 here: a 550 mm wave blade and 4.1 from 540 amazon.co.uk reviews. UK reviews describe a cleaner cut on mineral wool and on PIR around 50 mm. The same blade binds or wanders on 90–150 mm board, and several reviews say there is no guard. That is the top pick in this set of six, not a UK-wide ranking and not a lab test.
How much does an insulation knife cost on amazon.co.uk?
In this set the shelf prices on 19 October 2026 run from about £11.48 to about £19.99. The Predator is about £11.48 and the Trade 4 You single about £11.95. The Bahco PC-22-INS is about £15.92. The YHSC two-pack is about £18.50, the Everhard about £19.01, and the folding Bahco about £19.99. A UK dealer listed the long Bahco at £16.99 including VAT.
What should I check before I buy an insulation knife?
Match the edge to the material, then a blade length you can verify, then the sheath. Glass wool and rock wool suit a toothless or wave blade. Foil-faced PIR under about 50 mm can be scored and snapped, or cut with a serrated saw. A 550 mm wave saw is a different tool from a 3-5/8 in roofing knife. Ignore RPM or volts on a hand tool. A 5.0 from six shared ratings is a thin sample.
Can one insulation knife cut both loft wool and thick PIR?
Not cleanly, on the evidence here. The Predator is praised on glass-fibre roll and rock wool and doubted on foil board and Kingspan. The Bahco PC-22-INS is often fine around 50–70 mm PIR and mixed above about 75 mm. UK retail copy caps EPS and XPS at 75 mm. Keep a fine-tooth wood saw for long cuts in thicker PIR. The mineral wool insulation knife guide stays with quilt and slab.
Do I need a mask when I cut mineral wool?
Yes if the loft is dusty. Reviews say an insulation knife makes less dust than a wood saw. That is not a dust-free cut. ROCKWOOL’s UK data sheet gives a limit of 5 mg/m³ inhalable dust and 2 fibres/ml as 8-hour averages, and says to prefer a knife. FEF suggests an FFP1 or FFP2 mask when loft dust cannot be predicted. Do not dry-sweep wool dust, and do not cut material that might be asbestos.
Is it legal to buy a long insulation saw in England and Wales?
It is an offence to sell a knife to someone under 18 in England and Wales. A 190 mm folding saw or a 550 mm insulation saw is not the 3-inch non-locking pocketknife exception in section 141A of the Criminal Justice Act 1988. GOV.UK also covers carrying a knife in public and the good-reason test. A sheath does not change the age rule. Check the current GOV.UK page before you rely on a summary.
Is a polystyrene cutter the same as an insulation knife?
No. The Bahco retail line allows EPS and XPS up to 75 mm on the PC-22-INS, which is still a hand saw. A hot-wire polystyrene cutter is a different product. If you are shaping polystyrene rather than slicing loft wool or PIR, use the polystyrene cutter comparison. Do not trust an RPM or voltage figure on a hand insulation saw.
Our verdict
The Bahco PC-22-INS scores 88 in this set: about £15.92, a 550 mm wave blade, and 4.1 from 540 reviews. That is the top pick for mineral-wool slabs and PIR around 50–70 mm. It has no guard in the reviews that asked for one, and long cuts in 90–150 mm PIR bind or wander. The Spear & Jackson Predator scores 84 at about £11.48, with 4.2 from 122 reviews. That is the best value when the job is glass-wool roll or rock wool. The listing length is 350 mm and the maker states 270 mm. None of this is a lab test, and a 5.0 from six shared ratings is not a ranking.
Best value
View offer
Spear & Jackson B98INS Predator insulation saw
Score 84 at about £11.48, the usable fibre saw after the top pick is assigned, with 4.2 from 122 reviews.
Editorial
Editor, DIY & tools
Cutting toolsInsulation knivesamazon.co.uk listings
Peter F. is the editor for DIY & tools at productscompared.co.uk. Comparisons in this category are checked against amazon.co.uk listings, review evidence and public UK sources.
Updated: October 2026
8 sources checked
Guides to insulation knives
Guides on what to look for, how to use a product, and common mistakes.
Insulation knife buying guideEdge, length and material before you pick a brand.Best insulation knifeOne pick per job, and who should skip it.How to cut insulationMark, support, cut and sheath, with no ranking.Insulation knife for PIR boardFoil-faced rigid board, including Kingspan and Celotex.Insulation knife for mineral woolQuilt and slab with less tearing, plus a mask.
Related comparisons
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)
Expert source (DIY & tools): Charlie White (Charlie DIYte) (external profile) – public expert commentary used as a research source, not as a contributor to our pages.
This page contains affiliate links to amazon.co.uk with the tag pcuk26-21. If you buy through them, we may earn a commission at no extra cost to you. Prices, stars and review counts are the amazon.co.uk listing lines from 19 October 2026. We did not run a lab test.