The barriecoat of the Composite Slem line is a syntactic foam based on vinylester resin and low density mineral fillers, specifically formulated to be applied as a first layer after the gelcoat and thus act as a barrier to marking caused by the fibres and cores reinforcing the composite laminate. It represents an effective partial or total alternative to the first layer of manual MAT (skincoat) with significant advantages in terms of laminate construction speed.