3 Deformation and Thermal History Room temperature deformation is permanent. Plastics stretched at about Tg and cooled slowly are heat stable. Plastics stretched at about Tg and cooled quickly have “memory” and will shrink if reheated.3 Deformation and Thermal History Room temperature deformation is permanent. Plastics stretched at about Tg and cooled slowly are heat stable. Plastics stretched at about Tg and cooled quickly have “memory” and will shrink if reheated