Roofing felt is a type of material used in roofing systems to provide an additional layer of protection. It is typically made from fiberglass or organic materials, coated with asphalt to make it waterproof. Roofing felt is installed between the roof deck and the shingles, helping to prevent water infiltration and protect against leaks. There are two main types of roofing felt: #15 and #30, which refer to the weight of the felt per square. The heavier the felt, the more durable and resistant it is to tearing and weather conditions. Proper installation of roofing felt is essential for ensuring the longevity of a roof.