It is generally recommended to wash fabrics before sewing with them. This is because fabrics can shrink, bleed or change in texture after washing, and this can affect the fit and appearance of the finished garment or project. As a general rule of thumb, Cottons, Linens, Rayon, Viscose Fabrics should always be pre-washed to test shrinkage and colour runs.
Washing the fabric before sewing also removes any dirt, dust, or chemicals that may be present from the manufacturing process, which can improve the quality and longevity of the finished product.
However, there may be some exceptions to this rule. For example, some fabrics such as dry-clean only fabrics, may not be suitable for washing. Additionally, some fabrics like leather or vinyl may not be able to be washed at all.
It’s always a good idea to check the care instructions for the specific fabric before washing to avoid any damage or unwanted changes in texture or size.