The Complete Guide to Rash Guards, Dive Skins, and Thermal Underlayers

When preparing for a dive trip, most divers focus on the two main pieces of exposure protection: the wetsuit or the drysuit. But tucked away in the accessories section are the unsung heroes of dive comfort—the rash guards, dive skins, and thermal underlayers.

These pieces of light-duty exposure protection are crucial. They protect your skin from the sun's harsh UV rays, shield you from abrasive BCD straps and jellyfish stings, and, most importantly, they can dramatically boost your thermal retention without forcing you to buy a bulkier, more restrictive wetsuit.

For the traveling diver, these layers are essential for achieving maximum comfort and flexibility across various water temperatures. At Paragon Dive Store, we believe layering is the key to mastering thermal regulation. This guide will walk you through the differences between these layers and how to use them to customize your dive setup.

Rash Guards (The UV and Abrasion Shield)

A rash guard is the most basic, versatile, and essential piece of protective apparel for any water sport.

What It Is

A rash guard is a form-fitting shirt (long or short-sleeved) typically made from a blend of Lycra, Spandex, or technical polyester. They offer zero thermal protection on their own, but they serve three vital purposes for the diver:

• UV Protection (UPF 50+): When you are sitting on the dive boat for an hour surface interval, your skin is exposed to intense, direct sun. A high-quality rash guard provides UPF (Ultraviolet Protection Factor) 50+, blocking over 98% of the sun’s UVA and UVB rays. This is non-negotiable for sun-safe diving.
• Wetsuit Donning Aid: The smooth material of a rash guard minimizes friction between your skin and the sticky neoprene lining of your wetsuit. This makes sliding into your wetsuit significantly easier and reduces the wear and tear on the suit's interior.
• Abrasion/Sting Protection: While not heavy-duty, they offer protection from minor scrapes, BCD harness rub, and very light aquatic stings.

Best Use Case

• On the Boat: During surface intervals or while setting up gear.
• Under a Wetsuit: For easy donning and added comfort.
• Snorkeling/Swimming: In very warm water where you only need sun and sting protection.

Shop Our Selection of Rashguards

Dive Skins (The Full Body Barrier)

Dive skins are the full-body version of the rash guard and are engineered for specific tropical conditions.

What It Is

A dive skin is a full, head-to-toe jumpsuit made from the same Lycra/Spandex materials as a rash guard, often with a front zipper for easy entry.

• Primary Function: Stinger Protection: In tropical waters, particularly during certain seasons, divers can encounter invisible jellyfish larvae or stinging hydroids. A dive skin creates a physical barrier over the entire body, providing effective protection against these minor, painful stings.
• Minimal Warmth: While primarily for protection, the thin layer of material does prevent some water from flowing directly over the skin, offering a minuscule thermal benefit—perfect for water that is 80°F (27°C) or warmer.

Best Use Case

• Tropical Diving (80°F+): When you don't need a wetsuit for warmth but need protection from the marine environment.
• Under a Wetsuit (Layering Aid): For maximum ease of donning a wetsuit, especially one that is tight or has a sticky interior.

Thermal Underlayers (The Warmth Multiplier)

This category represents the highest value for the traveling diver who owns a thin (3mm or 5mm) wetsuit and wants to extend its comfort range.

What It Is

Thermal underlayers are specialty garments—often vests, long-sleeve tops, or shorts—designed to be worn directly against the skin under a wetsuit or drysuit. They work by trapping a thin layer of body-warmed water close to the skin.

• High-Tech Materials: Look for materials like Polar Fleece, polypropylene, or very thin (0.5mm to 1mm) neoprene. These materials are incredibly efficient at trapping heat relative to their minimal thickness.
• Key Items:
  • Hooded Vests: This is one of the most effective thermal upgrades you can buy. Since you lose up to 30% of your heat through your head, a thin, hooded vest that also covers the core is a powerful tool for adding warmth without restricting limb movement.
  • Fleece/Polypro Tops: Lightweight long-sleeved tops worn under the wetsuit for core and arm warmth.

Best Use Case

• Boosting a Wetsuit: A high-quality thermal underlayer can make a 3mm suit feel like a 5mm suit, or a 5mm suit feel like a 7mm suit. This is perfect for the Tucson diver who owns a 3mm tropical suit but travels to slightly cooler temperate waters (like the colder months in Mexico or California).
• Core Warmth: Excellent for deep dives where the water temperature drops significantly.

Explore Thermal Vests and Underlayers for Maximum Warmth!

The Ultimate Layering Guide: Making Your Wetsuit Work Harder

The real magic happens when you understand how to combine these layers based on your destination and the day’s dive plan.

Final Pro-Tips from Paragon Dive Store

1. Sizing is Key: All layers—especially thermal ones—must be snug to work properly. They are designed to hold water close to your skin. If they are baggy, cold water will constantly flush through, defeating the purpose.
2. Rinse Immediately: Lycra and Spandex are tough, but salt and chlorine will break down the fibers over time. Always rinse these layers immediately after the dive, just like your other gear.
3. The Thermal Trinity: If you want the biggest thermal boost with the least amount of bulk, invest in three items: a thermal hooded vest, good 5mm neoprene gloves, and good 5mm boots. This combination protects your heat-loss centers (head, hands, and feet) and makes a huge difference in comfort.

By understanding the unique properties of rash guards, dive skins, and thermal underlayers, you can stop fighting the cold and start customizing your exposure protection to perfectly match any environment you travel to.

Ready to gear up for your next trip? Explore our massive selection of layered protection accessories today!