Duralay Heatflow 15sqm Sponge Rubber Carpet Underlay: 6/6 Premium Durability, 5/6 Extra Comfort, 6.1mm Thick, 0.75 Low Tog, 1.33m x 11.33m Roll Suitable for stretch-fit installation of carpets. Designed specifically to complement under floor heating systems, allowing heat to easily pass through. Duralay Heatflow underlay was the first underlay specially developed for under floor heating under carpets. This 6.10mm textured flat, sponge rubber underlay has a low tog value of 0.75 tog enabling it to maximise the warmth & cosiness of your room, & reduce your heating costs.