Can the swim cap be 100% waterproof?
Swim caps are designed to reduce drag, protect the hair and help keep the head warm. However, they are not completely waterproof. Swim caps are made from materials like silicone, latex or lycra which are water-resistant but not completely waterproof. Some water can seep through the cap, especially around the edges where the cap meets the skin.
Swim caps are not designed to keep your hair or head completely dry, but rather to protect your hair from the harsh effects of chlorine and saltwater and to reduce drag while swimming.