Torch-down roofing used to be heated by a kettle and mopped on the roof. Modern day products are not put on the same way as this. Typically now a torch-down roof is a modified bitumen membrane that has been reinforced with a very high quality nonwoven polyester mat. When the proper amount of heat is applied it has one of the finest seals around today. This is used for residential and commercial roofing systems.
This type of roofing is used on roofs that have too low of a slope for shingles which is less than a 2:12 pitch. There are many roofing materials that are designed for these low slope roofs but few are as durable and long lasting as this type of torch-down. This is also considered a cool roofing type which simply means it helps with energy costs of your home.