Spandex itself does not have good waterproof properties. The main reasons are as follows:

• Molecular structure: Spandex contains more polar groups in its molecular chain segments, such as amino and carboxyl groups. These polar groups make spandex hydrophilic to a certain extent. Water molecules easily interact with these polar groups, so that water can penetrate into the spandex fiber to a certain extent.
• Fiber characteristics: Spandex fiber has high elasticity and flexibility, and its fiber structure is relatively loose, unlike some special waterproof fabric fibers that have a tight arrangement and structure. This loose structure makes it easier for water molecules to penetrate through the gaps between fibers.
• Practical application: In practical applications, spandex is usually not used as a fabric alone, but is blended with other fibers such as cotton and polyester to increase the elasticity of the fabric. In this blended fabric, even if other fibers have a certain degree of waterproofness, the presence of spandex will reduce the waterproof performance of the overall fabric to a certain extent.

However, through some special finishing processes, such as coating and lamination, the waterproof performance of spandex-containing fabrics can be improved to a certain extent, but this is not the waterproof property of spandex itself, but is achieved through external treatment.