Best Women’s Hiking Underwear: Why I Swear by Merino Wool
I first started looking at merino wool women’s hiking underwear for backpacking. After switching from a synthetic to a merino wool sun hoodie, I wondered if merino underwear would make a difference on the trail, too.
Synthetic underwear, even the best moisture-wicking varieties, always felt hot and damp to me. I wanted something I could comfortably wear all day.
My first multi-night backpacking trip with my new merino layers back in 2022 was a success. I wore my BRANWYN bra for four days while backpacking rim-to-rim through the Grand Canyon and tested a couple of pairs of BRANWYN underwear. No rubbing, no constant adjusting. They just worked.
Since then, I’ve sworn by merino wool for hiking underwear and layers. No more funky smells after days on the trail, and in my experience, the temperature regulation and moisture management are hard to beat.
Recently, I compared BRANWYN with three other popular merino wool underwear brands: Icebreaker, Smartwool, and Woolly. I wanted to see if anything better had come along since I first made the switch.
Spoiler: After four years of wearing BRANWYN and testing three alternatives, it’s still my favorite.
Affiliate Disclosure: This post contains affiliate links, which means I may earn a commission if you purchase through my links at no additional cost to you. I purchased all four brands of underwear with my own money. BRANWYN is offering me a gift card for publishing this review. All opinions are my own and based on my personal hiking and backpacking experience.
Wearing my BRANWYN matching set for hiking and swimming in Yosemite.
What Is the Best Women’s Hiking Underwear?
My favorite women’s hiking underwear is the BRANWYN Essential Bikini. I’ve worn mine regularly for four years without developing a single hole, and I love the comfortable, seamless construction.
While the other merino wool underwear I tested had their advantages, BRANWYN remains my top choice for hiking, backpacking, and everyday wear.
Merino Wool Women’s Hiking Underwear I’ve Tried
1. BRANWYN Essential Bikini (Best Overall)
I’ll be completely honest: if there’s one brand of merino wool underwear I stand behind, it’s BRANWYN.
What sets their performance innerwear apart is the seamless knit construction and single-layer gusset. There’s no separate elastic waistband rubbing against your skin and no bulky gusset stitching. The result is a smooth, comfortable fit without irritating seams.
I still wear my original pairs I purchased back in 2022 in addition to new pairs I’ve bought more recently. My lighter-colored underwear has faded from years of washing, but my black pairs have retained their color.
I’ve noticed a few areas where the fabric has started to thin, but none of my pairs have developed holes. They’ve also held their shape remarkably well, and I appreciate the consistent sizing. Newer pairs I’ve ordered fit just like my oldest ones. If you’re between sizes, I recommend sizing up for the most comfortable fit.
BRANWYN has been the underwear I reach for on every hike and backpacking trip. They’re comfortable under both hiking pants and shorts, and I never have to think about them once I’m on the trail. That’s exactly what I want from hiking underwear.
➡️ If you’re also looking for comfortable hiking bottoms, check out my guide to the best hiking pants for curvy women, where I share the pants I’ve tested and worn.
I personally prefer the bikini style, but BRANWYN also makes hipster, thong, and boyshort options.
One thing worth mentioning is that BRANWYN’s fabric feels thicker than some other merino wool blends I’ve tried. I suspect that’s part of why they’ve lasted so long, although I can’t say for certain.
2. Woolly Merino Underwear (Runner-Up)
The Woolly Women’s 95% Merino Wool Bikini Panties caught my eye because of their high merino wool content.
The fabric is incredibly soft, and I appreciate that the gusset is sewn down all the way around, so there’s no loose liner or awkward pocket. They fit like a traditional bikini, which I really like.
The biggest downside for me is the separate elastic waistband. Unlike BRANWYN, Woolly doesn’t have a seamless construction, so it’s not quite as comfortable for my preferences.
That said, these are a solid runner-up. If you want a soft, lightweight pair of hiking underwear with a high percentage of merino wool, Woolly is worth considering.
3. Icebreaker Merino 150 Siren Hipkini (Thinnest)
I was intrigued by the Icebreaker Women’s Merino 150 Siren Hipkini because its cut falls somewhere between a bikini and a hipster. After trying it, I’d say it fits much closer to a bikini.
Of all the merino wool hiking underwear I’ve tested, Icebreaker’s fabric feels the thinnest. So far, it’s held up well, but I’m curious to see how it performs over several years of regular use.
Like Woolly, Icebreaker has a separate elastic waistband, which isn’t my favorite. The front of the inner gusset also isn’t sewn down, leaving a loose edge that I personally don’t love.
Overall, it’s a good lightweight option, but I prefer the construction and fit of BRANWYN and Woolly.
4. Smartwool Merino Underwear (Returned)
I own several Smartwool products that I love, including my ultralight merino hoodie and warm base layers. So naturally, I thought I’d like the Smartwool Women’s Merino Bikini, too.
Before wearing them, I tossed them in the wash without thinking much of it. But when I pulled them out to hang dry, I noticed two holes in the fabric. I hadn’t even worn them yet! Needless to say, I was disappointed.
I decided to try them anyway and wore them a few times before ultimately returning them. Beyond the durability issue, I found the fit much lower-cut than the other bikini styles I tested. Some people might prefer that, but I like a more mid-rise fit.
I’m not suggesting that every pair of Smartwool underwear will develop holes. This was simply my experience with one pair, and because I returned them, I can’t speak to their long-term comfort or durability.
Merino Wool vs. Synthetic Hiking Underwear
Merino wool underwear isn’t cheap, no matter which brand you choose. I certainly didn’t buy six pairs all at once. Instead, I’ve built my collection over the years, purchasing one or two pairs at a time.
Synthetic hiking underwear is generally more affordable. Many synthetic fabrics are lightweight, quick-drying, and durable, making them a practical choice for backpacking.
There’s also been a growing interest in moving away from synthetic clothing in favor of natural fibers. While merino wool underwear often contains some synthetic fibers for stretch and durability, I appreciate its high wool content.
For me, the biggest difference is comfort. I’ve found that merino wool’s natural odor resistance and temperature regulation really do make a difference, especially on multi-day backpacking trips.
Ultimately, both materials work for hiking, but after years of wearing merino wool, I have no plans to switch back.
➡️ Merino wool is also my preferred material for hiking socks. If you’re looking to upgrade more of your hiking essentials, check out my guide to the best merino wool hiking socks.
How to Care for Women’s Merino Wool Hiking Underwear
Many merino wool underwear brands recommend gentle washing or hand washing to help preserve the fabric. I don’t know about you, but I don’t have time to hand wash my underwear!
Instead, I toss mine in the washing machine on the cold setting with my regular laundry and hang them to dry. I’ve been washing my BRANWYN underwear this way for over four years, and they’ve held up remarkably well.
BRANWYN recommends using a mesh laundry bag, which I haven’t bothered with. While following the manufacturer’s care instructions is the safest way to extend the life of your underwear, my experience shows that merino wool doesn’t necessarily have to be high-maintenance.
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FAQs About Women’s Hiking Underwear
Is Merino Wool Underwear Worth the Money?
In my experience, absolutely! Merino wool underwear costs more upfront, but my original BRANWYN underwear has lasted over years of regular wear without developing holes. I recommend starting with one or two pairs rather than replacing your entire underwear collection at once.
Does Merino Wool Underwear Prevent Chafing?
Merino wool helps manage moisture, which can reduce some of the conditions that contribute to chafing. However, it won’t prevent chafing entirely. Proper fit, comfortable seams, and keeping your skin dry are just as important. I’ve personally had great luck with BRANWYN’s seamless construction and haven’t experienced rubbing or irritation while hiking.
Is Merino Wool Underwear Itchy?
Quality merino wool underwear is generally much softer than traditional wool because merino fibers are finer. However, sensitivity varies from person to person. I’ve found the merino wool underwear I’ve tested comfortable against my skin, particularly BRANWYN and Woolly, which both feel soft to me.
Is Merino Wool Underwear Good for Hot Weather?
Yes! Merino wool is breathable and helps manage moisture, making it a good option for warm-weather hiking. I’ve found it more comfortable than synthetic underwear on hot, sweaty hikes. However, fabric thickness matters, and a thinner merino blend like Icebreaker or Woolly might appeal to hikers who prefer a lighter feel.
Can You Machine Wash Merino Wool Underwear?
It depends on the manufacturer’s care instructions, but many merino wool underwear products can be machine washed on a gentle, cold cycle. I personally wash my BRANWYN underwear in cold water with my regular laundry and hang it to dry. Although BRANWYN recommends a mesh laundry bag, I’ve had good results without one.
How Many Pairs of Underwear Should I Bring Backpacking?
For multi-day backpacking trips, I recommend bringing at least three pairs of underwear so you can rotate between them. Merino wool’s natural odor resistance makes it a great option for backpacking, but it’s still important to change into clean underwear regularly. You can also wash a pair on the trail when needed, following Leave No Trace practices.
For more tips on staying clean on the trail, check out my ultralight backpacking hygiene kit, where I share the toiletries and hygiene essentials I pack for multi-day trips.
