Buyers compare security film by thickness, because thickness is the number on the box. In practice, thickness only sets how much energy the film can absorb before it tears. Whether the glazing stays in the opening after an impact is decided somewhere else entirely: at the frame.
What each thickness is for
| Thickness | Typical use | What it does and does not do |
|---|---|---|
| 4 mil / 100 µm | Anti-spall, fragment retention on interior glass | Holds shards together after accidental breakage. Not an intrusion barrier. |
| 7–8 mil / 175–200 µm | Smash-and-grab resistance, commercial ground floors | Delays entry and keeps glass in one sheet. Without anchoring, the sheet can be pushed out as a unit. |
| 12–14 mil / 300–350 µm | Higher-risk retail, banks, forced-entry delay | Greater energy absorption, still dependent on frame retention and, usually, a structural silicone or mechanical anchor. |
The frame is the specification
A filmed pane behaves like a membrane. Under repeated impact the glass cracks, the film stretches, and the load transfers to whatever is holding the perimeter. If the film is simply cut to the glass edge and the glazing bead is a dry, snap-in type, the whole assembly can be displaced. Three common ways to prevent that:
- Wet glaze — structural silicone applied into the perimeter rebate, bonding film to frame. The most common retrofit method.
- Mechanical retention — a continuous metal or profile strip fixed over the film edge into the frame.
- Factory-applied or tested systems — the film and frame are supplied and certified together; usually only practical on new glazing.
Each adds labour and a visible edge detail. That cost is why "8 mil, anchored" and "8 mil, edge-cut" are not the same product, even at the same price per square metre.
Standards: what the words mean
Film is routinely described as "blast rated" or "safety certified". The claim is only meaningful against a standard and a tested assembly:
- ANSI Z97.1 / CPSC 16 CFR 1201 — safety glazing performance. A film applied to existing glass does not turn that glass into certified safety glazing unless the filmed assembly was tested as such.
- EN 356 — manual attack resistance, graded P1A to P8B.
- ASTM F1642 — glazing response to blast, reported with hazard ratings.
- ASTM F3561 — forced-entry resistance of fenestration systems.
If a supplier cannot name the standard and the assembly, treat the claim as marketing. Ask for the test report number and the glass build it was tested on: 6 mm clear monolithic behaves differently from a laminated sealed unit.
Specifying it properly
- Start from the threat: accidental breakage, opportunistic entry, or deliberate forced entry.
- Choose thickness from the threat, then choose retention from the frame type.
- Ask for test evidence on a comparable assembly — same glass, same frame, same anchorage.
- Price the anchoring separately so the client sees what the barrier actually costs.
A 4 mil anti-spall film on an interior partition is a sensible, cheap fix. An 8 mil film on a shopfront with a dry-glazed aluminium frame and no anchor is a false sense of security — and it is the most common specification mistake we see in enquiries.
