The Catalyst is the state-of-the-art in training paddle design. Unlike some paddles, the Catalyst improves all strokes while minimizing the risk of injury. It is constructed of durable, UV protected polypropylene that is injection molded for a smooth, pliable shape without sharp edges. Sizing Information: - XXS: Beginning swimmers - XS: Young age groupers (8-12 years) - Small: Older age groupers (12+), beginning Masters - Medium: Older High School males, Sr. National Females, mid-level masters. - Large: Collegiate swimmers, Sr. National males. - X-Large: Very strong swimmers, water aerobics.