ISO 20393:2007规定了通过扩散测定试样长期吸水率的设备和程序。它适用于隔热产品。它的设计目的是模拟产品在长时间内对水的吸收，不仅要经受两侧约100%的高相对湿度，还要经受水蒸气压力梯度，例如倒置的屋顶或无保护的地面隔热。 本试验不适用于所有类型的隔热产品。产品标准通常应说明该试验是否适用于特定产品。

ISO 20393:2007 specifies equipment and procedures for determining the long-term water absorption of test specimens by diffusion. It is intended for use with thermal-insulation products. It is designed to simulate the absorption of water by products subjected for a long period of time not only to high relative humidity, approximating to 100 %, on both sides but also to a water vapour pressure gradient, as experienced by e.g. inverted roof or unprotected ground insulation. The test is not applicable to all types of thermal-insulation product. The product standard should normally state whether this test is applicable to a particular product.