Treatment with a wash-in or spray-on waterproofing solution serves as the best way to give most cotton hats water-wicking properties. Often available at retailers that sell outdoor apparel, these commercial products create a temporary bond that repels moisture. Although various brands of waterproofing solutions operate on the same principles and share similar application methods, the products do vary. To be on the safe side, always read and follow any instructions or warnings the manufacturer provides.
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The Science of Waterproofing
Commercial waterproofing agents often take the form of liquid elastomers, or polymers that have elastic properties. Essentially, when the waterproofing liquid comes in contact with the cotton fibers of your hat, it fills in the spaces between those fibers to prevent water from penetrating. Instead of soaking the fabric, water that comes in contact with treated cotton beads and rolls off the surface. Because of their elastic nature, these agents keep the fabric flexible even when it's treated.
Wash In or Spray On
To begin the waterproofing process, always start with a clean hat to increase adhesion. If you have a washing machine-safe cotton hat, you can simply add a commercial cotton waterproofing treatment to the cycle in the amount recommended by the product's manufacturer. You can, of course, spritz a spray-on waterproofer onto the surface of the hat, using a damp sponge or cloth to help even out the application. Waterproofing agents that contain fluorocarbons require heat activation, which you provide by tossing your hat in the dryer. If you use a fluorocarbon-free product, you can air-dry your hat to set the treatment.
Keeping It Waxy
If you have a hat made of waxed cotton, also known as oilskin, the waterproofing process varies a bit. Because this textile has already been treated with wax, it repels water from the get-go. However, oilskin's waxy finish wears off over time and with use. When this happens, you must re-waterproof your hat with a wax-based reproofing cream or spray. The sprays work much like other waterproofing products, but the cream must be warmed and massaged into the fabric. In general, waxed cotton hats and other garments need re-waterproofing about once per year, but exposure to the elements accelerates the need. You should deal with shiny or uneven spots on the hat more often.
More to Soak In
Waterproofing agents are synthetic chemical products, so always check the label to ensure that the product is safe to use on cotton and on clothing. Because it bolsters the elasticity of cotton fibers, the application of a waterproofing treatment may actually strengthen the fabric, increasing its resistance to tearing. Though normally long-lasting, these treatments wear off after a certain number of washings. Longevity varies depending on your hat's exposure to the elements and per individual product.