Slim belts are basically elastic girdles — for lack of a better term. Prior to your workouts, you bind your waist with the belt to trap in heat. The heat increases your body temperature, which leads to better weight-loss results, according to the manufacturers. They're made from a variety of materials, but the most common is neoprene, a synthetic rubber.
Features Perfect elasticity. Breathable materials. No rolling over, no buckling.