Hygrometry is the science that seeks to determine the quantity of humidity contained in the atmosphere.
People often confuse the term relative humidity with the term hygrometry when referring to the quantity of humidity contained in the air.
Relative humidity plays an important role in the quality and ageing of structures made of composite materials in two different ways:
• during manufacture, the relative humidity is an important parameter to control in areas where draping or saturation is performed. In fact, the presence of humidity is detrimental during production;
• when in use, a composite structure always has a certain capacity for water absorption (about 0.5 to a few % in weight); in environments with high relative humidity the structure will absorb water, which will generally lead to a decrease in the mechanical strength of the laminate (following a decrease in the mechanical strength of the resin and in certain cases fibres, for example, kevlar) as well as a decrease in the resin's glass temperature transition temperature.
Extreme humidity should away be taken into account when sizing.