The proper wetsuit, rash guard, or scuba wetsuit makes the difference from a relaxed, comfortable dive and a distracted and unhappy experience. The rash guard (a term not often used outside dive circles) for warm tropical waters is a very lightweight garment, usually made of Lycra or a similar UV-blocking material, doesn't warm you as you dive but still protects from jellyfish, sea lice, and fire coral. A neoprene wetsuit ranging from 1-3mm thickness is great for temperate waters. A neoprene scuba wetsuit 5-7mm thick is great for colder waters. Wide variety of sizes, styles, and colors available - including special camouflage spearfishing wetsuits.
Your wetsuit, rash guard, or scuba wetsuit is what dive shops call exposure protection, which is a crucial part of your diving gear. Because your body loses heat much faster when you're underwater, the proper wetsuit makes your dive more comfortable and enjoyable. Choose a wetsuit thickness based on the water temperature you're diving in. For hot summer waters in tropical areas, a dive skin or rash guard protects you from sun and stings without making you sweat underwater. Neoprene wetsuit thickness ranges from 1-3mm for warm to temperate waters, up to 5-7mm for colder waters. For very cold temperatures, you may even want to consider a drysuit, which will keep your body completely dry. Your wetsuit prevents stings from sea pests such as jellyfish, sea lice, and fire coral. Depending on the water temperature you are diving in, there are full wetsuit options with long legs and sleeves, and shorty wetsuit choices (short sleeves and legs). Shorty wetsuits preserve core body heat while leaving your arms and legs completely unencumbered.