Hygroscopy

Chemical degradation caused by reaction with water, which breaks susceptible bonds such as the ester linkages in polyesters and some polyurethanes. Warm, humid conditions accelerate hydrolysis, which can degrade laminates, adhesives and membrane reinforcements over time.

The movement of water through a semi-permeable layer towards a more concentrated solution. In glass fibre hulls, water diffusing through the gelcoat can react with soluble substances in the laminate to form fluid-filled blisters, a defect widely known in the marine industry as osmosis or osmotic blistering.

The temperature region over which an amorphous or partly amorphous polymer changes from a rigid, glassy state to a softer, rubbery one. It sets a practical upper service temperature for resins and adhesives and can be reduced by absorbed moisture or incomplete cure.