Elastophene PS is an adhered base sheet membrane composed of SBS modified bitumen and a glass mat reinforcement.
Commonly referred to as mop base sheet this product is applied using hot asphalt on flat roofs on the field or for flashing details. A fuse welded bitumen cap sheet is then torch applied overtop of this sheet. The rolls are staggered at the centre of the roll when lined up with the cap sheet.
Details and specifications can be found at the link below.