Hugh Bradner, a University of California, Berkeley, physicist invented the modern wetsuit in 1952. Wetsuits became available in the mid-1950s and evolved as the relatively fragile foamed neoprene was first backed, and later sandwiched, with thin sheets of tougher material such as nylon or later spandex (also known as lycra). Improvements in the way joints in the wetsuit were made by gluing, taping and blindstitching, helped the suit to remain waterproof and reduce "flushing", the replacement of water trapped between suit and body by cold water from the outside. Further improvements in the seals at the neck, wrists, ankles and zippers produced a suit known as a "semi-dry".