Abstract: A prefabricated underlay material (1) for location between upper surface of a load-bearing floor (8) and a continuous surface material (9), which underlay material comprises a substantially flexible sheet material (2) and dampening projections (3) formed of porous resilient material on one surface of the sheet material and distributed along the surface. Dampening projections (3) comprise strips (13) of foamed polymer or polymer mixture bonded to a first surface (11) of the sheet material without deformation of the surface thereof, which strips are located continuous, or intermittently continuous, with intervals (S) and are either principally straight or substantially undulating.