A theory for stress relaxation is presented which applies when crazing is the mode of relaxation. The theory is in terms of the microparameters of crazing, which are the density, size, shape, and velocity of the crazes. The stress‐relaxation curves of polystyrene, polymethylmethacrylate, and polycarbonate were measured in nitrogen and helium environments at 77 K. PS and PMMA stress relaxed only inN2,which causes crazing. The PC stress relaxed inN2and He. The experimental stress‐relaxation curves from crazing agreed with the theoretical equation and the experimental curves were shown to be predictable in terms of the microparameters of crazing.