The modern flip-flop has a very simple design, consisting of a thin rubber sole with two straps running in a Y shape from the sides of the foot to the gap between the big toe and the one beside it. They typically do not have a strap around the heel, although heeled varieties are available, as well as flip-flops designed for sports, which come with added support common to athletic shoes, with the thong between the toes. Most modern flip-flops are inexpensive, costing as little as $5, or less in some parts of the world.
They are made from a wide variety of materials, as were the ancient thong sandals. The modern sandals are made of more modern materials, such as rubber, foam, plastic, leather, suede, and even fabric. Thongs made of polyurethane have caused some environmental concerns; because polyurethane is a number 7 resin, they can't be easily discarded, and they persist in landfills for a very long time. In response to these concerns, some companies have begun selling flip-flops made from recycled rubber, such as that from used bicycle tires, or even hemp, and some offer a recycling program for used flip flops.
Because of the strap between the toes, flip-flops are typically not worn with socks. In colder weather, however, some people wear flip-flops with toe socks.