We are talking about $80 (or more) T-shirts here, so this is valid question. I think merino T-shirts are worth the investment. They offer considerable benefits over cotton and other natural fibers, as well as synthetics. Merino offers great temperature regulation, excellent moisture wicking, and they don't smell, which means you can wear them more and don't need as many of them. Three merino T-shirts in your wardrobe will last you as many days as 10 cotton shirts, so from a financial angle it's a wash.
Here's a quick rundown of some of the benefits of merino wool:
Odor-resistant: One of merino wool's superpowers is that it’s naturally resistant to odors. This means you can wear a merino T-shirt multiple times before needing to wash it. How many times? I'd say that depends where you are and what you're doing, but usually three to seven times. Our top pick is, after all, called the 72-hour shirt, because that's how long you can generally wear it before it needs a wash. See below for more on this debate.
Thermoregulation: Merino wool can keep you warm in cold weather and cool in warm weather. Yes, there are limits to this—no T-shirt is going to keep you cool on a hot summer day in the tropics—but merino far outshines cotton and synthetics.
Moisture wicking: This is an important one for anything you're wearing while hiking or at the gym. Merino wool is excellent at moving moisture away from your skin, through the fabric, where it can evaporate quickly. This is why it makes such a good base layer.
Versatility: Merino wool shirts are great for travel, hiking, backpacking, and as everyday shirts for around town. They can also be used year-round, even in the cold, as part of a good layering system.
Packable: Merino wool T-shirts tend to pack up smaller than cotton and many synthetics, meaning they take up less room in your bag when traveling. Combine this with the odor resistance above and your have the ultimate travel T-shirt.
The one place cotton and nylon blend T-shirts might possibly have an edge is durability. Merino wool isn't really any less durable in my experience, but it can pill, which is where the wool fibers break and tangle together in tiny knots, forming little balls on your T-shirt. Some pilling isn't a big deal, but if a T-shirt pills a lot you know it's made of very made of short wool fibers, rather than longer continuous fibers.
Unfortunately, most manufacturers don't advertise the length of their spun fibers, which is where our testing comes in. I hate pilling, and I have eliminated all the T-shirts that have pilled on me, except one, which I like anyway (the pilling is not that bad).
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