Thermomolding for Distance

Thermomoldable ski boot liners are really cool.  They’ve yet to make it into many/any boots designed for touring (horizontal miles, rather than vertical), but they should.  They’re warm, act as a vapor barrier and don’t absorb much moisture, and with care and proper technique can be impressively flexible as regards fit, both for a variety of feet and a variety of fits for a single pair.

Conventional wisdom for downhill-oriented skiing has liners fitting quite close all around, including the toes.  Coming from a hiking background I was skeptical this could work without causing blisters and cold toes, but the last few years of fiddling has shown this to not necessarily be true.  My big boots have some Scarpa overlap thermos in them, and my toes just kiss the liners when they’re flat.  During normal skiing they’ve proven to be very comfortable, even below zero, even out all day.  The only shortcoming comes during extra-ski shenanigans, for example walking downhill for 2.5 miles at the end of yesterday’s outing, a lamentable set of circumstances due to a lack of snow low down and an unwillingness to kill my new skis.  The toe bang which ensued reminded me that after this trip I never got around to reshaping the liners in my TLT 1000s.  I leave tomorrow for a three day wolverine research trip, and the high for the whole time is right around 5 F.  No time like the last minute to make sure your toes don’t fall off.

There is a lot of internet discussion of cooking liners at home.  Having paid a shop to do it, and having done it myself, I don’t think there are too many disadvantages to a home oven.  Set it a hair below 250, the tray in the middle, and rotate the liners frequently.  Don’t burn them, and wait until they’re puffy and starting to really get floppy before you pull them out.

The name of the game when baking liners for distance-oriented touring is lots of toe room, and a snug fit elsewhere (especially the heel).  The only way to achieve the former is some seriously aggressive toe spacers.  Closed cell foam and duct tape gets the job done.  You want to create lots of space with this.

A thin sock, the sort you’ll want to use with thermos anyway, goes over the toe cap.  I got some ultralight merino ski socks from Patagonia recently (thanks Jackie) and thus far they’ve been very nice.  They do not fall down, and hopefully the high nylon content will make them more durable than the equivalent one-season socks from Smartwool.

Once you’ve rigged out your foot and placed the nice hot liner over it (stretch the liner to get it all the way over the heel), the next trick is to get it into the boot shell without causing wrinkles which will create pressure points later.  There are lots of ways to do this, but my approach is simple, quick, and effective: put a plastic shopping bag over your liner-ed foot, and right before you slide that in spray the inside of the shell liberally with cooking spray.  Do this and hold the shell open and you should have no problems.  Be gentle but not hesitant.

Once in, make sure the liner is settled as it should be, and buckle the boot gently.  You want the foam to expand as much as possible, to fill voids and thus facilitate a good fit and max insulation.  Stand on the foot (only do one at a time!) kick the heel in hard a few times, and aggressively wiggle your toes frequently.  I like to stand with about 1/3 body weight on the boot foot, with the toe set up on something 3-4″ tall.  Creating a bomber heel pocket and keeping plenty of toe space are the two goals here.

I like to let the whole rig cool pretty completely, about 15-20 minutes, before removing my foot.  Let the liner sit a further 10 minutes before removing it to get the grocery bag out.

You’ll be able to rebake if you got it wrong, but the process is involved enough that its nice to get it right the first time.

Old LaSportiva trail runner insoles: stock on left, modded for ski boot on right.

I put insoles in my ski boots, mainly to take up volume (my feet are top to bottom really skinny), but also to improve fit and add warmth.  One curious by-product of being accustomed to increasingly minimal trail shoes is that I no longer find arch support tolerable.  Both my ski boots, but these old T2s in particular, have more than I like.  I could get them punched out by a shop, but instead I modify the insoles to relieve this pressure, which seems to work pretty well.

The boots featured in this post are a bit ghetto, and while not ideal better for what I want them to do than anything commercially available.  The comments on my review of the Hok, and the article itself, discuss this in more detail.  They’re also, if you have access to a used gear store, pretty cheap.  Especially nice in the increasingly unaffordable world of backcountry skiing.

On a related note, Luc Mehl’s outstanding article on Fast and Light Winter Travel is now available on his site, for those without a BPL subscription.  Good inspiration to get out while what snow we’ll have is still around.

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2 thoughts on “Thermomolding for Distance

  1. Great idea for the toe spacers. I have wanted to use my thermo ski boot liners for ski boots for winter ultras at -40F (e.g., Arrowhead Ultra), but could never figure out how to make space for the swelling toes.

    I have a pair of T3, about the same vintage like your T2, circa 1997. To add extra warmth, I lined the inside of the plastic shell with aluminium tape. I also use anti-persiprant on my feet to keep my feet warm and dry.

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