Sock liners are thin wicking socks worn underneath a heavier hiking or snowsport sock. The biggest benefit they provide is blister prevention, particularly when you are wearing a stiff leather hiking, mountaineering boot or skiing boot that has very little give to it. They’re often not needed for softer synthetic boots or if you wear a low hiking shoe like a trail runner.
Sock liners prevent blisters in two ways: they wick moisture away from your feet which can lead to increased friction and they help prevent ill-fitting boots from rubbing your skin and causing a hotspot.
When you wear boots, your feet generate about half a cup of perspiration per day, which explains why your socks are often damp when you take your boots off. This is particularly true if you are wearing a mid or over-the-ankle hiking boot which traps this perspiration unlike a running shoe which is much better vented. Further, so-called breathable Gore-tex or other waterproof membranes cannot vent this much perspiration in a day and are easily overwhelmed, which is why your socks will still remain damp even if you’ve invested in a breathable boot.
Sock liners work like any other base layer by efficiently transporting, also called wicking, your perspiration to the next outer layer of your clothing system and away from the surface of your skin. Very thin, non-absorbent sock liners are the best for wicking sweat up to a thicker, outer sock.
Personally, I prefer wearing very thin synthetic liner socks, thin nylon business dress socks, or wool liner socks woven with a significant amount of nylon or spandex for this purpose. I’d had good luck with REI Coolmax Liner Socks, Gold Toe Nylon Dress Socks, and REI Wool Liner Socks, which have proven quite durable when worn under a thicker hiking or mountaineering sock. Whichever liners you choose (be sure to avoid cotton liners), they should be thin and well-fitting, without any bunching around the toes or rough seams that will irritate your feet.
Hotspots are precursors to blisters. They’re caused by friction, especially when your foot has too much room to move around inside your boots, your boots are too hard and not well broken-in, or you have an anatomical issue with your foot such as a bunion or hammer toe that rubs against the inside of your boot.
The function of socks is fill up the inside of your boots so your feet don’t slide around in them and to prevent a boot from rubbing your skin raw and creating hotspots. If you wear a soft mid or over the ankle hiking boot that’s made out of synthetic fabric, you can often get away with wearing a single hiking sock of medium to heavy thickness and not get any hotspots or blisters. Lighter snthetic boots like this have a lot more give to them than old-fashioned leather hiking or mountaineering boots which have little to no give at all.
For heavier boots, it’s best to wear a sock liner together with a medium to heavy sock, depending on the room available inside your boot. When you wear two socks with these harder boots, the boot rubs against the outer sock, but not the inner sock, which remains snuggly fitted around your foot. With two socks, all of the friction occurs between the two layers of socks and not between your sock and your skin, which is why the two sock system works so well.
This post was written in response to a reader question about sock liners, when to use them, and how a two-layer sock system can prevent blisters.
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