4 mil or 8 mil security window film
Updated: 21 October 2026
You are holding two clear rolls for the same side-light, one labelled 4 mil and one labelled 8 mil, and the thicker title looks like the safer buy. This comparison of 4 mil or 8 mil security window film is what those labels measure, how they sit next to National Protective Security Authority notes, and what the amazon.co.uk listings in this set actually state. The full table stays on the [security window film comparison](/hub/door-and-window-security/security-window-film). On 21 October 2026 Peter F. used captured shelf prices and public UK notes, not a lab measurement of these rolls. A qualifying purchase can earn a commission at no extra cost to you.
You are holding two clear rolls for the same side-light, one labelled 4 mil and one labelled 8 mil, and the thicker title looks like the safer buy.
You are holding two clear rolls for the same side-light, one labelled 4 mil and one labelled 8 mil, and the thicker title looks like the safer buy. This comparison of 4 mil or 8 mil security window film is what those labels measure, how they sit next to National Protective Security Authority notes, and what the amazon.co.uk listings in this set actually state. The full table stays on the security window film comparison. On 21 October 2026 Peter F. used captured shelf prices and public UK notes, not a lab measurement of these rolls. A qualifying purchase can earn a commission at no extra cost to you.
Our top picks
| Badge | Product | Thickness | Named test | Roll size | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  Buydecorativefilm BDF S4MC 4 mil | 4 mil | ANSI Z97.1 Class B | 91 cm × 7.32 m | 8.6 | about £66.51 | View offer |
 Mgood Mgood 4 mil, 30 cm | 4 mil | None | 30 × 200 cm | 8.0 | about £11.59 | View offer | |
 Qualsen Qualsen 8 mil, 30 cm | 8 mil | None | 30 × 200 cm | 6.8 | about £19.98 | View offer |
On this page
What 4 mil and 8 mil measure
One mil is one-thousandth of an inch, about 25.4 microns, so 4 mil is about 100 microns and 8 mil is about 200 microns. Several listings also write 4 mil as about 0.1 mm. Treat the figures as about: they convert the seller’s label, and these rolls were not gauged. A side-light sold as 4 mil is about a tenth of a millimetre of film. An 8 mil label on the same width is about twice that polyester.
The Glass and Glazing Federation counts thickness as the polyester layers only, and leaves out the adhesive and other coatings, so two 4 mil titles can still differ once the glue is on the glass. AWKAQUN states no mil, and reviewers call that roll very thin, so it does not sit on the 8 mil side. Qualsen’s thicker title is a claim of about 200 microns of polyester, not a UK impact class.
The NPSA steps are microns plus a certificate
National Protective Security Authority note EBP 08/13 is blast guidance for annealed glass, not a household chart of 4 mil against 8 mil. Film identified as Class 2(B)2 shall be at least 100 microns and shall be certificated to BS EN 12600 Class 2(B)2. About 100 microns without that certificate is only a thickness. Where bomb-blast net curtains are omitted, except for very small panes, the same note says Class 1(B)1 film of about 175 microns should be used instead. That sentence can include a thinner film, or a multi-layer film, when it has enhanced properties. An amazon title that says 8 mil, about 200 microns, is not that class by the number alone.
EBP 09/13 asks you to check a current impact certificate, because an older one may not match today’s film and adhesive. Trade pages sometimes map their own 100 micron films to EN 12600 2B2 and their own 200 micron films to 1B1 or EN 356 P1A. Those certificates are not Qualsen’s 8 mil listing and not the 4 mil rolls here. An EN 356 class is a manual-attack result for a built-up system, not a mil on a carton.
What this set actually lists
Clear 4 mil film is the common label here. Narrow rolls at 30 × 200 cm include Mgood at about £11.59, DARUITE at about £11.89, and Qualsen at about £12.57. Wider 4 mil sheets are a width choice on the best security window film page. As arithmetic from the stated size, those narrow rolls work out at about £19 to £21 per square metre, a rule of thumb from the 21 October 2026 capture, not a live quote.
Qualsen 8 mil is the same 30 × 200 cm size, captured at about £19.98, with 3.4 from five ratings, and it names no test. Ultraviolet protection is marked true with no percentage, so there is no UV figure to quote. On about 0.6 square metres, about £19.98 is a higher shelf price than those narrow 4 mil rolls. Compared with them, it is a thicker small roll, and it is not a wider sheet. BDF S4MC is the top pick and the only listing that states a test, and it states it on 4 mil film: 100 micron in the highlight, ANSI Z97.1 Class B and CPSC Category 1. Those are United States safety-glazing tests. They do not make 4 mil the certificated UK thickness, and they are not BS EN 12600 or BS EN 356. The best value in the wider comparison is a mid-price 4 mil roll, not this 8 mil label.
When thickness will not decide it
In this set, choose the 8 mil label only when you want Qualsen’s thicker claim on a 30 cm roll and you accept five ratings and no named test. Choose a 4 mil roll when that width covers the pane in one piece and you are buying the common clear film, not a class. If the pane is wider than 30 cm, thickness will not fix a seam. A 70 cm kitchen pane is still short of a 30 cm roll whether the film says 4 mil or 8 mil. If the glass is rough, frosted, or already laminated, neither mil belongs on it.
Thickness is the wrong question when you need a current certificate, an insurer’s blast note, or a PAS 24 window. The NPSA steps are for certificated film on annealed glass, not a reason to treat an 8 mil title as Class 1(B)1 or BS EN 356 P1A. A thicker sheet is harder to squeegee, and cure time depends on thickness and temperature, so this page does not give a day count. The order of checks is in the security window film buying guide. For a named UK class, leave both labels and ask a glazier.
Common questions
How many microns is 4 mil, and how many is 8 mil?
4 mil is about 100 microns, and 8 mil is about 200 microns. One mil is one-thousandth of an inch, about 25.4 microns, and several listings also write 4 mil as about 0.1 mm. The Glass and Glazing Federation counts the polyester layers and leaves out the adhesive and other coatings, so the title is not a measurement of the full stack. Neither figure is a UK class on its own. These rolls were not gauged for this page.
Is thicker always the better security film?
A thicker polyester claim can mean a heavier sheet than a 4 mil label, though this set was not tested that way. Qualsen’s 8 mil roll is the thicker label here and it names no test. BDF, the top pick, states ANSI Z97.1 Class B and CPSC Category 1 on a 4 mil roll. Those are United States safety-glazing tests, not a reason to treat 4 mil as the certificated UK thickness. If you need a certificate, the mil on the title will not supply it.
Does 100 microns mean NPSA Class 2(B)2?
No. National Protective Security Authority note EBP 08/13 says film identified as Class 2(B)2 shall be at least 100 microns and shall be certificated to BS EN 12600 Class 2(B)2. About 100 microns on an amazon title is the seller’s thickness claim. It does not certificate the 4 mil rolls in this set. The note is blast guidance for annealed glass, not a badge you can read off the mil.
Does 8 mil mean Class 1(B)1 or BS EN 356 P1A?
No. About 200 microns is a thickness. Class 1(B)1 in the NPSA note is about 175 microns when blast curtains are omitted, and the film still has to be that class. A thinner film can qualify if it has enhanced properties. BS EN 356 P1A is a manual-attack class of a built-up system, not a mil number. Qualsen’s 8 mil listing states neither class.
What does 8 mil cost in this set, and what is missing?
Qualsen 8 mil, 30 × 200 cm, was about £19.98 on amazon.co.uk in the capture, with 3.4 from five ratings. The same size in 4 mil was about £11.59 to £12.57. The 8 mil listing names no impact test, and ultraviolet protection is marked true with no percentage. A per-square-metre comparison is arithmetic from the stated size, a rule of thumb from that capture, not a live price.
Why does the roll with a stated test say 4 mil?
BDF S4MC is 4 mil, with 100 micron in the highlight, and it is the only listing here that names a test: ANSI Z97.1 Class B and CPSC Category 1. That test sits on the thinner label. It does not make every 4 mil roll certificated, and it is not BS EN 12600 or BS EN 356. The roll is 91 cm by 7.32 m, captured at about £66.51, so it is a large sheet rather than the answer to one 30 cm side-light.
Related pages
Sources
Public UK sources for glazing and window security, last checked on 21 October 2026. Shelf prices, stars, and review counts are from the amazon.co.uk listings in this category on that date.
- Metropolitan Police: window security (retrieved 21 October 2026)
- Approved Document Q, 2015 (retrieved 21 October 2026)
- Approved Document K (retrieved 21 October 2026)
- GGF Datasheet 5.18.3: adhesive-backed polymeric film (retrieved 21 October 2026)
- GGF Datasheet 5.18.8: installation on existing glass (retrieved 21 October 2026)
- NPSA EBP 08/13: anti-shatter film (retrieved 21 October 2026)
- NPSA: security of domestic windows (retrieved 21 October 2026)
- EWFA technical paper on safety films (retrieved 21 October 2026)