Coremat is a nonwoven, based on polyester fibres with a binder system that contains microspheres. It is used as at thin core (bulker mat) or print blocker (liner) in fibre reinforced laminates, manufactured in Hand Lay-Up or Spray-Up processes. Coremat should always be fully impregnated with resin. The microspheres in Coremat prevent excessive resin up-take. The most important reasons to use Coremat are: Weight saving, Resin and glass saving, Stiffness increase, Fast thickness build-up.

Coremat as a core material is used in the center of a laminate. Coremat can replace much heavier solid glass layers. Impregnated Coremat has a density of 610 kg/m3 (38 lb/ft2), while Impregnated Chopped Strand Mat has a density of 1,500 kg/m3 (94 lb/ft3). This is a weight saving of 60%.

Coremat saves resin and glass; Coremat contains less resin than CSM: 1 mm (0.039 inch) of Coremat contains 0.6 kg/m2 (2.0 oz/ft2) while 1 mm (0.039 inch) of CSM contains 1 kg/m2 (3.31 oz/ft2).