Application Guide
Tamper-Evident Security Overview
How visible tamper evidence works and which construction suits which application.
Available on request
Tamper-Evident Release Films
Level 4 Heat-Sensitive Tamper-Evident Release Film
Tamper-evident release film manufactured entirely in house, carrying permanent VOID transfer plus a heat indicator that changes from white to pink when heat is applied to the seal.
At a glance
- Heat indicator
- White to pink on heat exposure
- Indicator reversibility
- Permanent — does not return to white
- VOID message transfer
- Permanent, on removal attempt
- Custom message
- VOID, STOP, TAMPERED BAG or your own wording
- Production
- 100% in-house Level 4 manufacturing
Overview
A determined attempt on a sealed bag usually starts with a heat gun. Warm the seal, lift it slowly, close it again, and a VOID-transfer construction alone can be defeated by patience. Level 4 answers that directly.
The construction carries a thermochromic indicator stripe. It reads white in normal handling and turns pink the moment heat is applied to the seal — permanently. The attempt is recorded before the bag is even opened.
Everything the Level 3 construction does is still present: permanent VOID transfer on removal, eight-colour gravure printing of your own message, red and blue as standard, 27 to 45 mm slit widths, and 100% recyclable LDPE. The heat indicator is added on top, not swapped in.
The whole construction is produced within PROASP — 100% in-house Level 4 manufacturing — which is what allows the layer structure and the evidence response to be developed per application rather than accepted as supplied.
Performance benefits
Heat-assisted attempts are recorded
The indicator stripe changes from white to pink when heat is applied to the seal, and does not change back.
Every Level 3 feature included
Permanent VOID transfer, custom printed messaging, red and blue standard colours and 27 to 45 mm widths all carry over.
Manufactured entirely in house
100% in-house Level 4 manufacturing keeps the construction under direct process control.
Two independent evidence signals
Heat shows on the indicator, lifting shows as VOID transfer. Defeating one does not defeat the other.
100% recyclable LDPE
The higher security level does not cost the recyclability of the closure.
Developed for the application
Layer structure and evidence response are built around the package the film has to protect.
Available configurations
- Evidence response
- Heat indicator — white to pink
- Permanent VOID transfer
- Security face cuts
- Width
- 27 mm
- 30 mm
- 35 mm
- 45 mm
- Or to your requirement
- Colour
- Red
- Blue
- Custom colours to requirement
- Message
- VOID
- STOP
- TAMPERED BAG
- Custom wording and artwork
Applications
- High-security packaging seals
- Cash-in-transit and bank deposit bags
- Evidence and chain-of-custody bags
- Aviation and duty-free security bags
- Pharmaceutical and controlled-goods packaging
How it works
01
Sealed
The film closes the bag. The indicator stripe reads white.
02
Heat applied
Heat is applied to the seal in an attempt to lift it without visible damage.
03
Indicator turns pink
The thermochromic stripe changes from white to pink, marking the seal as heat-exposed. The change does not reverse.
04
VOID revealed on lifting
If the seal is lifted anyway, the layered construction transfers a permanent VOID message across the separated layers.
Heat-indicator demonstration
When applicable security constructions are exposed to heat, the indicator changes colour to create visible evidence of the attempt. If the seal is lifted, the layered construction reveals a permanent VOID message.
View the demonstrationThe material in application
Production and application photography of this construction. Nothing here is a mock-up.
The indicator stripe on the reel, between the printed bands. 
One seal was warmed. The stripe turned pink and stayed pink. 
TAMPERED BAG printed as the transfer message on a blue construction. 
Lifting the seal transfers the message across both separated layers.
Technical specifications
Final suitability should be confirmed through technical discussion and application testing.
| Property | Value | Status |
|---|---|---|
| Heat indicator | White to pink on heat exposure | Standard |
| Indicator reversibility | Permanent — does not return to white | Standard |
| VOID message transfer | Permanent, on removal attempt | Standard |
| Custom message | VOID, STOP, TAMPERED BAG or your own wording | Custom |
| Security face cuts | Available | Available |
| Production | 100% in-house Level 4 manufacturing | Standard |
| Property | Value | Status |
|---|---|---|
| Material | 100% recyclable low-density polyethylene (LDPE) | Standard |
| Standard widths | 27, 30, 35 and 45 mm | Standard |
| Other widths | Slit to your requirement | Custom |
| Standard colours | Red, blue | Standard |
| Printing | Up to eight-colour gravure | Standard |
| Activation temperature | Confirmed per constructionPublished only once verified for the construction being supplied. | On enquiry |
| Core size and roll length | Confirmed against your sealing equipment | On enquiry |
How to read these values
- Standard
- Supplied as standard for this product.
- Available
- Available as an option on applicable constructions.
- Custom
- Made to your specification.
- On enquiry
- Confirmed against your application rather than published as a universal figure.
Documents and downloads
Frequently asked
Anything not covered here, ask the team directly — application questions are usually faster to answer than to document.
Ask a technical questionWhat exactly happens when heat is applied?
The thermochromic indicator stripe changes from white to pink. It is a permanent change: cooling the seal does not turn it back. That means a heat-assisted opening attempt is recorded on the packaging whether or not the person succeeds in lifting the seal.
What is the difference between Level 3 and Level 4?
Level 3 is the permanent VOID transfer construction — everything on this page except the heat indicator. Level 4 adds the white-to-pink thermochromic stripe on top of it. Nothing is removed to make room; Level 4 is Level 3 plus heat detection.
At what temperature does the indicator change?
The activation temperature is confirmed against the construction being supplied rather than published as a single figure, because it is specified to the application. Request it with your enquiry and the current verified value for that grade will be provided.
Is it really manufactured in house?
Yes — 100% in-house Level 4 manufacturing. The construction is produced within PROASP rather than bought in and converted, which is what allows the layer structure and evidence response to be developed per application.
Is the recyclability the same as Level 3?
Yes. The film is 100% recyclable low-density polyethylene in both constructions. The heat indicator does not change the base material.
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Discuss Level 4 Heat-Sensitive Film for your application
Send your substrate, dimensions, operating conditions and estimated volume. The enquiry form arrives pre-filled with this product so you only need to describe the application.