Plastic boots hold huge advantages for backcountry ski touring. And I mean true touring: multi-day trips where the travel is the primary goal. Plastic boots don’t absorb water, are somewhat to very waterproof, and the closed-cell foam liners you’ll find on any decent boot provide excellent insulation. Most importantly, CCF does not absorb more than trace amounts of the water. The liner mesh laminated onto any modern liner will, but a very modest amount. And of course plastic boots are the only option for serious, technical downhill.
The problems with plastic boots are twofold, and both have to do with the rigidity of plastic itself. Previous concerns about range of motion while going uphill or along the flat have been largely done away with by recent developments, but the difficulty of making feet comfy in rigid containers remains. This can only be addressed by a shell which mimes the foot shape well enough, and a liner molded properly.
I have wideish but thin (top to bottom) feet with a very narrow heel, and that second attribute has made getting a good snug liner fit with the Siderals a bit tough. The ultimate solution, which has been discussed for some time, is to sell shells and liners separately. We’re not there yet.
Pictured above is the stock 28 Sideral liner at left, and a 29 Scarpa overlap liner at right. I purchased the Scarpa liner on sale a few years ago, and molded it to fit in my 28 Scarpa T2 shells. That extra foam, crammed in to the smaller shell, took up all the volume in my midfoot and left a snug but comfortable fit. I skied the Scarpa liners in the Sideral shells once, and while the downhill performance was as good or better, the range of motion was so inhibited as to make an entirely different boot. The chief virtue of the stock liner is the zone of thinner foam which wraps the ankle front to back, and enormously increases fore and aft flex. For a shell like the Sideral, such a liner is absolutely vital, anything less defeats the purpose of the boot.
The problem for me is that the foam in the stock liner is pretty thin, and didn’t puff up all that much when heated. Heel hold and general support is adequate, but without significant help my midfoot was swimming, and the lower buckle had to be crushingly tight. I played with various insoles in and out of the liner, eventually settling on an insole of flat and very hard 1/4″ foam under the liner. A size 29 Intuition Protour liner baked down would be ideal, but until I’m willing to spend that money the foam will get the job done.
With that sorted, the Siderals have been great boots. They go uphill and downhill well, and are pretty darn good on the flats. The workmanship has thus far been impeccable. My favorite feature is the lower buckle, pictured above. The buckle itself has three teeth for tension adjustment, and the opposite side attachment (for the wire) has two slots, making it easy to find the sweet spot for foot hold. The ridges on the tongue allow for varied placement of the two wire strands, which is quite effective for fine tuning tension to suit individual preferences. On a boot like this the lower buckle is doing all the work anytime you’re not locked in to downhill mode, so the ability to make fine adjustments of this type is crucial for comfort.
In short, while I haven’t put enough miles into them to have a final judgment, thus far I’m pleased with the investment. For more detailed pictures and weights, look at my initial post here.