What makes a garment wrinkle-free? One of the more popular treatments is formaldehyde. Formaldehyde resins have been used to treat textiles, particularly cotton since the 1920s. Formaldehyde treatments are usually applied to combat wrinkling, improve stain resistance/colorfastness, and prevent mildew. Essentially, it has been used to make apparel fabrics easier to care for, transport, and manufacture over the last 100 years.