Chopped strand mat or CSM is a form of reinforcement used in glass-reinforced plastic. It consists of glass-fibres laid randomly across each other and held together by a binder.

It is typically processed using the hand lay-up technique, where sheets of material are placed in a mould and brushed with resin. Because the binder dissolves in resin, the material easily conforms to different shapes when wetted out. After the resin cures, the hardened product can be taken from the mould and finished.

Using chopped strand mat gives a glass-reinforced plastic with isotropic in-plane material properties.