A short John wetsuit is designed for use in warmer waters, typically during the summer months. It is a blend of a regular shorty and a long john style of wetsuit. It is a sleeveless top with shorts on the bottom so you have as much freedom of movement as possible to allow for strong paddling. Since there is no resistance from the neoprene against your arms you won’t tire out as quickly as you would with a sleeved version.
Designed specifically for summer surfing most people wear this type of wetsuit when the water temperature is around 72F (22C) depending on their personal taste. If you’re worried about sunburn on your arms you can always add a rashguard under the short john wetsuit for added protection.
The neoprene thickness in this type of wetsuit is normally about 2 millimeters with flatlocked seams. This means it won’t be completely waterproof which most surfers like when in warmer waters of the summer.
If you want to learn more about which wetsuit goes with which water temperature and what are the factors that influence the feeling of cold check this article.