How to Choose a Rash Guard

What Is a Rash Guard? How to Choose the Right One

Whether you're catching waves, logging laps, or spending a long day at the beach with the family, a rash guard is one of the simplest ways to stay comfortable and protected in the water. Originally developed by Australian surfers in the 1970s to prevent skin irritation from waxed surfboards and wetsuit seams, rash guards have since become essential gear for swimmers, paddlers, snorkelers, lifeguards, and anyone who spends extended time outdoors near water.

This guide covers everything you need to know — from how rash guards work and what they're made of, to choosing the right fit, sleeve length, and fabric for your activity. We'll also explain the difference between rash guards, swim shirts, and sun shirts so you can pick the best option for how you actually spend your time in the water.

What Is a Rash Guard and What Is It Used For?

A rash guard (also called a rashie or rash vest) is a thin, fitted shirt designed to be worn in and around water. The name comes from its original purpose: guarding against the rash caused by rubbing against surfboard wax, sand, and rough ocean surfaces.

Today, rash guards serve three main functions:

Sun protection. Most quality rash guards carry a UPF 50+ rating, which means the fabric blocks about 98% of the sun's ultraviolet radiation. Unlike sunscreen, a rash guard doesn't wash off, break down in the water, or need reapplying every two hours. It delivers consistent protection for as long as you wear it.

Skin protection. The snug fit creates a smooth barrier between your skin and abrasive surfaces — surfboard decks, pool walls, life vest straps, sandy shorelines, and even jellyfish stings. Flatlock stitching on quality rash guards means the seams sit flat against your body instead of overlapping, which eliminates one of the biggest sources of chafing during long sessions.

Comfort and performance. Rash guard fabrics are engineered to be lightweight, quick-drying, and stretchy enough to move with you. They don't absorb much water (typically less than 10% of their weight), so they won't feel heavy or drag you down the way a regular cotton t-shirt would.

Who should wear a rash guard?

Rash guards aren't reserved for surfers. They're practical for anyone who spends time in or near water:

Surfers and paddleboarders rely on them to prevent board rash and sunburn during multi-hour sessions. Swimmers and lap trainers wear them for UV coverage during outdoor pool workouts. Snorkelers and divers use them for reef protection and warmth in tropical waters. Lifeguards on duty all day benefit from the all-day UPF 50+ coverage that doesn't fade with sweat or water exposure. Families at the beach put them on kids (and themselves) for hassle-free sun protection that doesn't require constant sunscreen reapplication. And anglers and boaters appreciate the quick-drying, lightweight coverage on long days under open sky.

UPF vs. SPF: Why Fabric-Based Sun Protection Matters

One of the most compelling reasons to wear a rash guard is sun protection, and it helps to understand why fabric-based UPF protection often outperforms sunscreen alone.

SPF (Sun Protection Factor) measures how well sunscreen protects against UVB rays only — the rays primarily responsible for sunburn. UPF (Ultraviolet Protection Factor) measures how much of both UVA and UVB radiation a fabric blocks, providing broader-spectrum coverage.

Rash Guard vs. Swim Shirt vs. Sun Shirt

These three terms get used interchangeably, but there are real differences in fit and function. Choosing the right one depends on your activity and how you prefer a top to feel on your body.

Bottom line: If you're surfing, paddleboarding, or doing anything active in the water, go with a rash guard — the snug fit keeps the fabric in place and reduces drag. If you want easy, comfortable coverage for pool days and beach lounging, a swim shirt is the better pick. Sun shirts are great for on-land activities where breathability matters more than water performance.

What Are Rash Guards Made Of?

Most rash guards are made from a blend of synthetic materials — typically 80–90% nylon or polyester combined with 10–20% elastane (spandex). This blend gives the fabric its signature stretch, durability, and quick-drying properties.

Nylon vs. polyester

Nylon blends tend to feel softer against the skin and offer slightly more stretch. They're a good choice if comfort is your top priority. Polyester blends are generally more chlorine-resistant and hold their color better over time, making them the better option for swimmers who train regularly in pools. Many brands now use recycled polyester (often from recycled PET plastic) without sacrificing quality or technical performance.

Construction details to look for

Flatlock seams: The fabric edges are sewn together side-by-side without overlapping. This creates a smoother seam that lies flat against the skin and won't cause chafing during paddling, swimming, or surfing. This is the single most important construction feature to check when shopping for a rash guard.

Board short connector: A small loop sewn into the hem that attaches to your board shorts, keeping the rash guard from riding up during surf sessions.

Raglan sleeves: These extend in one piece from the collar to the underarm, providing a wider range of motion for paddling and swimming strokes.

How to Choose the Right Rash Guard

1. Decide on fit: snug vs. relaxed

A rash guard should fit like a second skin — close to the body without restricting movement. This snug fit minimizes drag in the water, prevents the fabric from riding up, and ensures the UV protection stays consistent (loose fabric can shift and expose skin underneath). If you prefer a more relaxed feel for casual beach days, look for a swim shirt instead.

2. Pick your sleeve length

Long sleeve: Maximum sun coverage on arms and shoulders. Best for long surf sessions, tropical travel, midday sun, and anyone who wants to minimize sunscreen application. Most popular for serious water sports.

Short sleeve: Covers shoulders and upper arms while allowing more airflow. A good balance for warm weather when you want some protection without overheating. Popular for pool swimming, beach volleyball, and casual use.

Hooded: Full coverage including the back of the neck, ears, and scalp. Excellent for anglers, boaters, paddleboarders, and anyone spending all day on open water under direct sun.

3. Check the UPF rating

Always confirm that your rash guard has a UPF 50+ rating — this should be clearly stated on the product label or description. Not all rash guards are UPF-rated, and vague claims like "sun protection" without a specific UPF number should be a red flag.

4. Match the fabric to your activity

For ocean and surf: prioritize stretch, durability, and a secure fit. Look for polyester-elastane or nylon-elastane blends. For pool training: choose chlorine-resistant fabrics (usually polyester-based) that hold their shape through repeated exposure. For casual beach use: a lighter, more breathable fabric works well, especially in hot climates.

5. Consider color

Lighter colors reflect more sunlight and keep you slightly cooler in intense heat. Darker colors may absorb more heat but are less likely to become translucent when wet. For visibility in open water — especially important for kids — bright or high-contrast colors are safest.

Women's rash guards often include additional features like zip-front closures for easy on-and-off, built-in shelf bras for support, and cropped styles. Browse women's rash guards to see what fits your activity.

Men's rash guards tend to come in standard crew-neck fits with options for board short connectors and thermal linings for cooler water. Shop men's rash guards for the full selection.

What to Wear Under (and With) a Rash Guard

A rash guard is designed to be worn as a base layer — you don't need anything between it and your skin. Here's how to pair it depending on your activity:

Surfing or paddleboarding: Wear the rash guard directly over your skin, paired with board shorts. If the water is cold, layer the rash guard under a wetsuit to prevent the neoprene from chafing.

Swimming (women): Most women wear a bikini top, sports bikini, or one-piece swimsuit underneath. If you want built-in support, look for rash guards with a shelf bra or pair with a supportive swim top.

Swimming (men): Wear directly over skin with swim trunks, jammers, or board shorts. No undershirt needed.

Beach and pool casual: Layer over any swimsuit. A zip-front rash guard makes it easy to throw on and take off without messing up your hair or pulling over sunscreen-coated skin.

Best Rash Guard by Activity

How Should a Rash Guard Fit?

A rash guard should feel snug and smooth — like a second skin that moves with your body. You don't want loose fabric that will billow with water, create drag, or ride up over your midsection. At the same time, it shouldn't be so tight that it restricts your breathing or range of motion.

Use your chest measurement as the primary sizing guide. If you're between sizes, size down for water sports where a secure fit matters (surfing, paddling) or size up if you prefer a less compressive feel for casual use.

Check the torso length. A rash guard that's too short will ride up every time you lift your arms or paddle, exposing your lower back to the sun. Look for styles with an extended hem or a board short connector loop to keep it in place.

Sleeves should hit your wrist bone (for long sleeve) without bunching. Sleeves that are too long will collect water and feel heavy. Raglan-cut sleeves generally offer the most natural range of motion for overhead strokes.

How to Care for Your Rash Guard

A well-cared-for rash guard will last multiple seasons. Here's how to keep yours performing at its best:

Rinse immediately after every use with cool, fresh water. Salt, chlorine, and sand will break down the fabric over time if left to sit. Don't wad it up wet and throw it in a bag — rinse it as soon as possible.

Hand wash with a mild soap or swimsuit-specific cleaner. Avoid bleach, fabric softener, and harsh detergents. Turn the rash guard inside out before washing. If you must machine wash, use cold water on the gentlest cycle.

Air dry only. Hang it in the shade on a plastic or wooden hanger (wire hangers can leave marks). Never put it in the dryer — high heat damages the stretchy fibers and degrades the UPF coating. Avoid drying in direct sunlight.

Store flat or on a hanger. Don't fold tightly or cram into a drawer. Avoid storing in hot cars, which can weaken the fabric over time.

For a deeper dive on maintenance, see our full guide: How to Care for Rash Guards.

Frequently Asked Questions

Methodology: This guide combines hands-on product testing by our gear review team, input from competitive swimmers and surf instructors, UV protection data from industry standards (ASTM F6544, AS/NZS 4399), and customer feedback from over 10,000 verified rash guard reviews on SwimOutlet.com.