What to Wear for a Half Marathon: A Temperature-by-Temperature Guide

What you wear on race day affects your race more than most runners expect, chafing, overheating, and blisters can undo months of training in the first few miles. The good news is that dressing right isn't complicated once you build it around two things: the forecast and what you've already tested in training.

Rule Zero: Nothing New on Race Day

Before the temperature chart, one rule overrides everything else: every piece of clothing and gear you wear on race day should already have miles on it from training. New shoes, new socks, a new sports bra, a new shirt, any of these can cause a blister, a hot spot, or chafing you've never dealt with before, and 13.1 miles is a bad place to discover it for the first time.

For shoes specifically, aim for 20 to 30 miles of prior use before race day. That's enough to confirm the fit is right and break in the upper, but not so many miles that the cushioning has started to break down. If you're shopping for race shoes, buy them at least three to four weeks out so you have time to log those miles in training.

What to Wear by Temperature

Use this as a starting point and adjust based on wind, sun exposure, and how you personally run warm or cold. Most runners should dress for how they'll feel once they're moving, not how they feel standing still at the start.

A few adjustments that matter more than the raw number on the thermometer: wind cuts effective temperature well below the forecast, so add a layer on a windy morning even if the number alone looks mild. Direct sun exposure on an exposed course pushes your comfort range up several degrees compared to a shaded route. And if the forecast is genuinely uncertain, the guide to handling unpredictable race day weather covers contingency planning beyond just what to wear, rain, heat spikes, and last-minute forecast changes.

Chafing Prevention: Where and How

Chafing comes from repeated friction against wet or damp skin, and it shows up in predictable spots:

• Inner thighs — especially in warm weather or longer distances where friction has more time to build
• Underarms — from arm swing rubbing against a shirt seam or the body
• Sports bra line — where the band sits against the ribcage for hours
• Nipples — a common problem for men running in a singlet or thin shirt without a chest seam

Apply an anti-chafe balm, Body Glide and plain petroleum jelly are both widely used and effective, to these spots before you get dressed, not after you start feeling discomfort. Choose moisture-wicking synthetic or merino wool fabrics over cotton; wet cotton against skin is one of the most common chafing causes because it holds moisture instead of pulling it away. If you're trying a new piece of clothing, test it on a long training run first, since chafing risk depends heavily on individual fit and can't always be predicted from the fabric alone.

Throwaway Layers for a Cold Start

If the forecast is cool at the start but expected to warm up, or if you'll be standing in a corral for 20-30 minutes before the gun, a throwaway layer solves the classic overdressing problem. An old sweatshirt, long-sleeve shirt, or even a garbage bag with head and arm holes cut out works fine, since you're planning to shed it anyway.

Wear it over your race outfit at the start, then remove and discard it in the first mile or two once your body has warmed up, ideally right around when you'd naturally finish your pre-race warm-up routine. Many large races collect discarded clothing along the first mile and donate it to local shelters, so check your race's website if you'd like to use official donation bins rather than dropping gear along the road. This approach solves the single most common wardrobe mistake: dressing for the cold corral and then overheating by mile 5 because you kept every layer on.

Socks and Footwear

Beyond the shoes themselves, invest in moisture-wicking running socks, synthetic or merino wool, not cotton, since damp cotton socks are a major cause of blisters. Trim your toenails a few days before the race, not the morning of, to avoid nicking a nail bed right before 13.1 miles on your feet.

Weather Accessories Worth Packing

A short list of accessories that solve specific weather problems rather than general comfort:

• Gloves for temperatures under 50°F; you can always stuff them in a pocket once your hands warm up
• A hat or visor for sun exposure on exposed courses, or a warm hat for cold starts
• Sunglasses for bright morning sun, particularly on east-facing or coastal courses
• Sunscreen applied before the race for any race starting after sunrise, reapplied if the race includes an aid station stop long enough to do so
• Reflective gear — a vest, reflective bands, or a headlamp — for races with a pre-dawn start where you'll be running in low light

Frequently Asked Questions

What should I wear for a half marathon if it's cold at the start but warms up?

Dress for how you'll feel about 15 to 20 minutes into the run, which usually means feeling slightly chilly standing in the corral. Use a cheap, disposable throwaway layer, an old sweatshirt or a garbage bag with head and arm holes cut out, that you can shed in the first mile or two once your body heats up. This avoids overdressing and overheating by mile 5, which is a more common mistake than being underdressed.

How do I prevent chafing during a half marathon?

Apply an anti-chafe balm like Body Glide or plain petroleum jelly to high-friction spots before the race: inner thighs, underarms, the sports bra line, and nipples for men running in a singlet. Choose moisture-wicking synthetic or merino fabrics over cotton, since wet cotton against skin is one of the biggest chafing causes. Test any new clothing on a long training run first, since chafing risk depends heavily on individual fit.

Should I wear new running shoes on race day?

No. Race day shoes should have at least 20 to 30 miles on them already, enough to confirm fit and break in the upper, but not so many that the cushioning has worn down. Brand-new shoes can cause blisters or hot spots you've never dealt with before, and worn-out shoes lose the cushioning your legs are trained to expect over 13.1 miles.

What temperature is too cold or too hot to run a half marathon in?

Most runners perform best somewhere in the 40s to 50s Fahrenheit, and racing gets progressively harder for pace and comfort as temperatures rise past the mid-60s. There's no fixed cutoff where a half marathon becomes unsafe, but heat above the mid-70s or heavy humidity meaningfully increases the risk of overheating and dehydration, so adjust your pace expectations rather than your effort level on hot race days.