A modified Nylon 6 formulation, developed originally for reaction injection moulding, has been used to freeform small parts. Liquid monomer is deposited as a fine stream from computer-controlled writing head and polymerizes on a heated plate as the part is built up. This is the first example of rapid prototyping of a linear polymer by direct polymerization. Nylon was chosen for this work because it attains good mechanical properties at relatively low molecular weights, so limiting the extent of chain propagation necessary. Freeformed bars were made with a strength of 75 MPa and tensile modulus of 2.3 GPa.