American alpine climbing expert Colin Haley gives a LOT of thought and serious field testing to his alpine clothing system. The Patagonia website has a superb deep-dive article that covers a lot of Colin’s clothing choices, some of them quite unconventional.

• Here's the original article on the Patagonia website.

• In case that goes away, here’s a PDF saved on my Google Drive.

For me, here are a few takeaways from this excellent article.

• “At any given moment in time, I must be able to wear every item of clothing that I brought with me on a climb (the exceptions to this rule are gloves and socks). The total insulation value of all my layers worn at once must be great enough for the environment I’m climbing in. A good rule of thumb for myself is that if I bring enough clothing to be comfortable for all planned circumstances (while belaying at night, for instance), then I’ll have enough warmth to make it through an unexpected circumstance, like an unplanned open bivouac. I wouldn’t by any means be comfortable, but I would feel safe from hypothermia.”

• “Highly technical climbing requires a very large range of motion (much more than trail running or skiing, for instance), and the ideal clothing system is the one that hinders that movement the least. Your clothing system should not only allow you to have full range of motion, but it should do so without wasting energy. For example, many soft-shell pants allow you to highstep, but you have to dramatically stretch the fabric every time that you do, and when you add up the thousands of times over the course of a big alpine climb that you highstep, you are wasting a lot of energy repeatedly stretching that fabric.”

• “When the wind gets strong (as it tends to do in high mountains, especially in Patagonia), not having an outer layer to block the wind drastically reduces the insulation value of the rest of your clothing. Whether or not you need a waterproof layer depends on the environment and circumstances in which you’re climbing. In a really cold environment, like on Denali or on 8,000-meter peaks, a waterproof layer is usually superfluous. In a place where the temperature often fluctuates right around freezing, a waterproof layer can be very important. Wind protection is essential in any high-alpine environment, and water protection might be important or might not be.”

• “Rather than bringing a heavier, warmer puffy, my preferred system is usually to bring two Micro Puff Jackets. When it’s warm, they’re both in my pack. When it’s chilly I wear one, and when it’s cold I wear both of them. I used to bring one in size S and one in size M, but I realized more recently that I prefer to bring both in size M. The baggier fit gives me better freedom of movement when climbing.”

• “The Houdini jacket is, in my opinion, the single most useful, important item of clothing that I own. It is very simple: just an incredibly lightweight windbreaker.”

• The Nano-Air vest has become one of my favorite items of clothing in the past couple of years. I find that a vest is often a great way to slightly boost the total insulation of a clothing system. Because a vest covers your torso it makes a significant difference to how warm you feel. Because a vest doesn’t cover your arms, it doesn’t affect freedom of movement much, and is thus well suited to technical climbing.

• “I used to nearly always get my jackets in the hooded version. More recently, I have decided that I prefer to have fewer hoods. The way I see it, if you can’t comfortably wear all of your hoods at the same time, then clearly you have too many! These days I prefer to have a bit more insulation directly on my head (often two balaclavas at once—see below), and only a couple of hoods. I feel that I have an easier time moving my head around this way.”

• “Recently, I have been using a system of two balaclavas: one is a very thin silk-weight, and the other is thicker and warmer. Unless it is really warm out, I wear the silk-weight balaclava for essentially the entire climb. It adds a bit of warmth and protects my ears and neck from the sun. Between my helmet, the silk-weight balaclava and my sunglasses with nose-guard and cheek-guards, I pretty much don’t have to use sunscreen at all, except on my lips. Whenever it gets colder, I put the thermal-weight balaclava on over the silk-weight one, and together they both fit comfortably under my helmet.”

• “Contrary to what many beginners might think, in a given pair of boots your feet will almost always be warmer in thinner socks, and colder in thicker socks. If your socks are too thin, then your boots will be too loose, and the climbing performance will be diminished. If your socks are too thick, your circulation will be reduced, and your feet will be cold.”