If you’re going to spend time in colder conditions, you might already be thinking about layering. It can get pretty bulky, and if you’re wearing several layers, it can be downright uncomfortable, not to mention laborious to disrobe. That’s why it’s time to invest in merino wool long underwear, a thin base layer that can keep you warm and eliminate the need for multiple layers.

Merino wool long underwear can be made of 100% wool or a blend. Both types provide superior warmth and comfort compared to traditional fleece or thick outerwear. Since the long underwear is designed to be a base layer, it’s easy to wear under a pair of jeans or pants all day. As a matter of fact, the long underwear is so comfortable, it’s used by outdoor enthusiasts, people who work outside, and the average person spending time in low temperatures. And unlike other garments and outerwear, it can last for years if it’s well cared for.

Stay warm in style with some sleek merino wool long underwear. Here’s our buying guide with the rundown on what to look for, including some of our favorites.

Merino wool comes from sheep, and sheep produce large amounts of lanolin that coats the wool to protect it from the elements. As a result, merino wool naturally repels moisture, provides UV protection, and is one of the least combustible textiles. It also has high tensile strength, making it incredibly durable. Merino wool is naturally odor resistant, so it’s a favorite among outdoor enthusiasts and professionals who work in all climates.

Merino wool is a natural insulator. You might be surprised to know that despite its seemingly tight weave, it has microscopic holes to be breathable. That’s why merino wool is considered an all-season, all-climate textile. It’s capable of keeping you warm in cold temperatures and comfortable in warmer environments.

When you shop for merino wool long underwear, you’ll see a number associated with the fabric. Grams per square meter (gsm) is the weight of the wool on a scale of 0 to over 250. Even if the weight isn’t apparent in the description, manufacturers will usually offer the grams per square meter to simplify things.

• Very lightweight wool: Less than 150 gsm

• Lightweight wool: 160 to 190 gsm

• Mid-weight wool: 195 to 250 gsm

• Heavyweight wool: 250 gsm and higher

You can find merino wool long underwear in men’s, women’s, and unisex sizing. For the most part, it’s easy to find big and tall sizes for men’s long underwear, which isn’t always true for other clothing. Some brands provide the inseam length, which is important if you’re tall. You want the underwear to be long enough to keep you warm, including your ankles. Styles that utilize inseam sizing tend to be a little more expensive, but at least you’re guaranteed a better fit.

Women’s sizes run the gamut as well, but it’s harder to find plus-size long underwear. As far as unisex sizes, these don’t always provide the greatest fit, though sometimes this long underwear is less expensive than gender-specific sizes.

Most merino wool long underwear is black or ivory. Certain brands offer a wider color assortment, especially those that have caught on to the trend of wearing long underwear as outerwear. In addition to plenty of solids, you’ll also find stripes and camo-themed options.

Merino wool long underwear is made from either 100% merino wool or a blend containing wool.

• 100% merino wool: In terms of quality, all-wool long underwear is superior because you get all the benefits of wool without being derailed by inferior materials. As a result, 100% wool long underwear is far more expensive than other types.

• Blends: Merino wool long underwear made of a blend usually includes around 30% merino wool combined with cotton, Lycra, spandex, polyester, acrylic, and/or silk. Each material offers something different, though they also take away from the qualities of pure merino wool. Cotton, for example, is a soft, breathable material, but it holds onto moisture. Some consumers feel long underwear made of blends doesn’t have the same tensile strength as 100% wool and is more susceptible to wear and holes.

Merino wool long underwear costs between $15 and $100, and more often than not, people buy two at a time to alternate between washings.

Inexpensive: The least expensive merino wool long underwear includes blends with about 35% merino wool. These cost between $15 and $35.

Mid-range: This long underwear may be 100% merino wool and costs between $35 and $55. Long underwear in this price bracket is also well constructed, true to size, and generally more comfortable.

Expensive: If you’re willing to spend closer to $100, you can find top-quality 100% merino wool long underwear. These garments far outlast their inexpensive counterparts, making them well worth the higher price.

• Give merino wool long underwear to an outdoor enthusiast. Merino wool long underwear is a useful, thoughtful gift for the avid hiker or camper in your family.

• Wash long underwear separately. Even though merino wool long underwear is machine washable, it’s a good idea to wash it separately so you don’t accidentally include it in a load with fabric softener.

• Look for long underwear with flat seams. If you have sensitive skin, opt for a style that features flat seams to reduce chafing and keep skin irritation to a minimum.

• Pack light. If you’re going on a trip to a cold destination, you can pack light by relying on merino wool long underwear to keep you warm. You won’t need as many bulky items, so packing a pair or two can save a lot of space in your luggage.

We like the 7EVEN Base Layer Bottom. Made from 100% ultra-fine merino wool (190 gsm) imported from Australia, this odor-resistant, hypoallergenic men’s long underwear is a quality investment at a modest price. If you’re partial to colors other than black, you’ll enjoy this light heather gray. Consumers who work outdoors give this product high marks for moisture wicking and comfort. If you’d like some ultra-comfortable 100% merino wool long underwear, the Minus33 Kancamagus Mid-weight Bottom (230 gsm) is ideal. Enjoy a broad color selection with this brand, including canary yellow, camo, and red. This garment is extra soft for all-season wear, an essential part of an outdoor wardrobe. It’s machine washable and dryer-friendly for easy, effortless care, too. If you prefer a pair with loose ankles, you’ll love the extended ankle panels that are almost 4 inches long.

Q. Will I be warm enough with merino wool long underwear, or do I also need matching tops and socks, too?

A. It really depends on your preference and where you’ll be. Having a 100% merino wool base layer neck to toe will undoubtedly keep you warm. If you feel like that’s too much, you can stick with your regular tops, socks, and outerwear. With that said, if you’re spending a lot of time outside and don’t have sufficiently lined footwear, it’s not a bad idea to invest in merino wool socks as well.

Q. How do I fix a hole in merino wool?

A. If you intend to sew it up yourself and you’ve never done it before, you’ll need the right needles, thread, and probably an online tutorial. It’s not an intimidating project, but it requires time and patience so the wool doesn’t pucker at the repair site. You could take it to a tailor if the cost to repair it is reasonable and less than the price of a replacement. Another option is to contact the manufacturer and see if the garment is covered under any warranty or satisfaction guarantee.

Q. What’s the best way to wash merino wool long underwear?

A. Each manufacturer details recommended care instructions on the label. As a general rule, it’s recommended that you wash the long underwear in warm or cool water with regular laundry detergent. Stay away from products that include bleach or other harsh chemicals, and refrain from using fabric softener. While some merino wool garments indicate that you can put them in the dryer, you can extend the life of the garment by simply air-drying it.