A roofing membrane underlayment material includes a fibrous mat generally encapsulated within a non-adhesive asphalt coating, the resulting encapsulated mat having an adhesive asphalt layer applied to one surface thereof, typically the bottom surface. An acrylic, talc or granular coating is applied to the surface of the encapsulated mat that is not in contact with the adhesive asphalt layer. The non-adhesive asphalt coating is characterized in that it includes a high filler content made possible by the use of non-oxidized flux asphalt to which has been added a small percentage of an asphalt additive such as radial or linear polymer or other elastomer. The resulting membrane, when applied to a roofing deck, provides a high traction surface that will not adhere to shingles and provides an effective waterproofing seal on the roofing deck and is flexible in both hot and cold environments.