Polymers with an all-carbon backbone, such as polyolefins, are usually resistant to hydrolysis. Condensation polymers like polyesters, polyamides, polyurethanes and polycarbonates can be degraded by hydrolysis of their carbonyl groups, to give lower molecular weight molecules. Such reactions are exceedingly slow at ambient temperatures, however, they remain a significant source of degradation for these materials, particularly in the marine environment. Swelling caused by the absorption of minute amounts of water can also cause environmental stress cracking, which accelerates degradation.