Abstract: A process for producing a polyurethane plastics having photochromic properties, characterized in that the process comprises in a first step incorporating a reversible cleavage photochromic compound into at least one di-isocyanate compound or at least one polyol or a mixture of a di-isocyanate and one or more polyols or into any other component of a mixture which, when polymerized, will yield a polyurethane; combining the mixture from the first step with any other necessary components to enable polymerization to occur; and polymerizing the resultant mixture to form a polyurethane incorporating the said photochromic compound. The photochromic polyurethane plastics of the invention are useful as intermediate layers in glass or plastics laminates for architectural applications or for use in vehicle windows or roof-lights.