Torch-on membranes are thick, polymer-modified bitumen sheets heated with a torch so they melt and fuse to the surface and to each other, creating a continuous, fully bonded waterproof layer that is far more robust than thin coatings.
The resulting membrane typically lasts 15–25 years, resists ponding water, UV, temperature swings and puncture, stays flexible enough to cope with building movement, and performs especially well on large flat or low-slope roofs, terraces and foundations when installed by experienced applicators.