Sauna suits are track suits made of a non-breathable material, leading to extreme sweating and subsequent dehydration. Boxers and wrestlers wear them prior to weighing in so that they can be classified in lighter classes, but many a casual jogger has taken to donning rubber or vinyl suits with the idea that they encourage quick weight loss. Which they do — it’s just that it is only water loss which is returned to the body upon drinking water. They also can be dangerous. The trend has even encouraged some fitness enthusiasts to wrap themselves in cling wrap or garbage bags during workouts; the next time you hear someone crinkling on the treadmill, remind them to drink some water.