Backpacking Underwear for Men: Types and Health Benefits Explained

Two pairs of the wrong underwear can turn a three-day trip into a chafing nightmare by mile eight. The fabric you pick decides whether you’re rinsing gear every night or wearing the same pair twice without gagging, and the difference between merino and synthetic comes down to what your trip actually demands.

REI’s hiking underwear guidance points to two practical categories for men: merino wool or merino blends for odor resistance and temperature regulation, and synthetics for faster drying at a lower price. Briefs, boxers, and boxer briefs are the main styles, and cotton is the one fabric to leave at home — it holds sweat, dries slowly, and rubs skin raw under a pack strap.

Why Fabric Choice Matters More Than Style

Moisture-wicking, quick-drying underwear keeps sweat off your skin and cuts the dampness that leads to chafing on long climbs. REI notes that breathable, formfitting underwear reduces bunching and rubbing under a backpack — the two problems that end trips early.

The health angle is straightforward: damp skin plus friction plus hours of walking equals raw, irritated skin. Merino wool is naturally odor-resistant and handles a wider temperature range, which is why thru-hikers wear it for days between washes. Merino blends add nylon, spandex, or TENCEL lyocell to improve durability and next-to-skin softness while keeping the performance that made wool popular in the first place.

Synthetics like nylon and elastane blends dry faster than wool and hold up well to daily washing. For hot, humid, high-output days — or trips where you rinse gear every night — a synthetic boxer brief often outperforms merino on dry time alone.

Merino vs. Synthetic: Which Type Fits Your Trip?

The honest answer depends on how often you plan to wash. Multi-day trips with infrequent laundry favor merino; sweaty day hikes and wash-every-night routines favor synthetics. Here’s how the two stack up against the specs that matter.

Real spec sheets show how blends work in practice. REI Co-op Merino Boxer Briefs run 49% merino wool, 30% TENCEL lyocell, 15% nylon, and 6% LYCRA spandex with a 6-inch inseam and a fly opening. ExOfficio Give-N-Go Sport Mesh Boxer Briefs skew synthetic at 89% nylon and 11% elastane. Ridge Merino Men’s Merino Wool Boxer Briefs sit at 83% merino, 12% recycled nylon, and 5% spandex — close to Ibex’s Natural Boxer Brief at the same blend and a 175 GSM fabric weight. Others spread wider: Patagonia Essential Boxer Briefs use 48% merino, 32% TENCEL lyocell, 15% nylon, and 5% LYCRA spandex, while Smartwool Merino Boxer Briefs reviewed by OutdoorGearLab are listed at 88% merino and 12% nylon.

Construction details matter as much as fiber content. Flat seams, tagless waistbands, a close-but-not-tight fit, and a fly option on some boxer briefs all cut irritation under a hipbelt. For most backpackers, a boxer brief is the recommended style because it balances coverage with chafe control. If you want a head start on specific models, this roundup of tested backpacking underwear picks narrows the field.

Merino’s reputation isn’t universal. Hiking guidance notes synthetic fabrics can beat merino on dry time and often work better for very sweaty, high-output use. Price reflects the trade too — Arms of Andes Boxer Briefs run $55 and the Ibex Natural Boxer Brief is $60, while synthetics typically cost less.

Common Mistakes That Cause Chafing

The most frequent error is wearing cotton on trail. REI advises against it because cotton doesn’t wick or dry well — it soaks up sweat and stays wet, which is exactly what you don’t want against skin under a pack.

Loose underwear is the second trap. Fabric that bunches shifts and rubs with every step, and a scratchy tag or raised seam under a hipbelt or waistband can turn a small annoyance into a blister-like sore. Fit should be close but not tight — snug enough to stay in place, with full range of motion.

One more thing to check before buying: “merino” rarely means 100% wool. Most backpacking underwear blends in nylon, spandex, or TENCEL for durability and stretch, and specs vary by model and year. Confirm the exact blend, inseam, fly, and care instructions on the product page before you commit.