If your boat is stored in a moist environment you will want to choose a fabric that is breathable like an polyester or acrylic that has not been coated, but rather, had treatments applied to the thread itself, sometimes referred to as solution dyed. A cotton fabric is the most breathable, yet the least durable fabric and not water resistant. If your boat will be subject to lots of rain, look for a polyester or acrylic fabric that has been coated with a moisture resistant compound. For boats that are subject to lots of sunlight, look for a boat cover fabric that has been treated with UV coating. Learn more about boat cover fabrics and other common boat cover questions at Go2marine.com.