DUAL OVERLAY by WARMUP 2.88m2. 7mm free floating smooth sub-floor over underfloor heating for Carpet, Vinyl Sheet, Karndean, Amtico & Vinyl Click. The 2 layers(3mm & 4mm) protect the heater wire from sharp or heavy point loads and provides an even heat distribution. Contact adhesive bonds the 2 boards together. Installation is quick, easy and dry. pack:4 x 4mm base & 4 x 3mm top boards, 1200mmx600mm. MDF boards with interactive adhesive