Lycra Swimming Cap. Since Lycra is a fabric, these caps will allow water to flow through the material while swimming. A permeable LYCRA CAP material is not as efficient as silicone or latex, but will still reduce drag to a greater extent than wearing no cap at all. Because of this, Lycra swim caps are not ideal for use in competition but are an excellent choice for young children who dont like the firm compression of a silicon or latex cap on their head and are suitable for Long Hair.