Short answer
TLX Silver is a BBA-certified multifoil fitted under the rafters (or across studs) as insulation, an airtight layer and the vapour control layer in one. It is the warm-side product; TLX Gold is the manufacturer's breathable over-rafter membrane. Silver is normally combined with PIR or wool between the rafters to reach a target U-value.
- Under the rafters, warm side
- Acts as the airtight VCL when taped
- BBA certified since 2006
- Pair with PIR or wool between rafters
- TLX Gold is the over-rafter, breathable product
What it is
A thin multifoil quilt of reflective films interspersed with wadding, with welded (not stitched) seams and a very low compressed thickness, manufactured in the UK by TLX Insulation. The manufacturer describes it as a 2-in-1 insulating vapour barrier: it adds thermal resistance and, taped and continuous, provides the airtight vapour control layer on the warm side of the roof. It has held BBA certification since 2006 and LABC registered detail status.
Where it goes
- Under the rafters, pulled taut across the underside and fixed with battens (the manufacturer suggests 38 × 38mm) that form the reflective air space and the service void.
- Across the face of timber studs in walls, on the warm side.
- Not over the rafters as a cold-side layer: like other vapour-resistant multifoils it would trap moisture there. The manufacturer's over-rafter product is TLX Gold.
Typical build-ups
- TLX Silver under the rafters with PIR between them, leaving an unventilated air layer between the PIR and the quilt and the ventilation or breathable membrane above the PIR. The manufacturer indicates around 70mm of rigid insulation between rafters to reach a 0.18 target in a standard roof; the exact figure comes from its calculation for the specific build-up.
- TLX Silver under the rafters with mineral wool between them — the manufacturer states no air gap is needed against wool because it is vapour-open.
- Room-in-roof: Silver across slopes and stud walls as one continuous airtight layer.
TLX Silver vs TLX Gold
| TLX Silver | TLX Gold | |
|---|---|---|
| Role | Insulating vapour control layer (AVCL) | Insulating breathable membrane |
| Position | Under rafters / warm side of studs | Over rafters, under tile battens |
| Vapour behaviour | Vapour-resistant, airtight | Vapour-open |
| When fitted | From inside, any time | Re-roof or new roof |
| Replaces | Separate VCL | Breather membrane |
| Used together? | Yes — Gold over, Silver under, insulation between, is a manufacturer-described hybrid roof | |
Pros
- Very thin when compressed, so minimal headroom loss with a 38mm batten.
- Long-standing BBA certificate and the manufacturer publishes the BBA-measured R-value rather than a marketing figure.
- Welded seams; taped, it forms a complete airtight VCL.
Limitations
- It is a vapour barrier: placed on the cold side it causes the condensation it is meant to prevent, and building control may reject such a build-up.
- Its own resistance is modest; a target is normally reached with PIR or wool between the rafters.
- Downlighters and services cut through the layer must be sealed or the airtightness is lost.
Alternatives
SuperFOIL SF19+ and SOPREMA SuperQuilt are the comparable under-rafter multifoils with integrated VCL; PIR board with a taped foil face where a fixed-depth single product suits. Vapour control guide.
Independent of the manufacturer. A home assessment measures the rafters and specifies Silver, Gold, a hybrid or an alternative — then quotes it.
Questions homeowners ask
Is TLX Silver breathable?
Does TLX Silver go over or under the rafters?
Does TLX Silver meet building regulations on its own?
Can TLX Silver and TLX Gold be used together?
- TLX Insulation — TLX Silver technical documentation — checked 2 September 2026
- BBA — Agrément certificates search — checked 2 September 2026
- LABC — Registered details and product assessment — checked 2 September 2026