Introduction
Very cold weather creates a variety of problems for the hiker, and still more for the backpacker. Cold feet can be (at best) a discomfort and, in the worst case, a major health risk resulting in frostbitten toes and feet. Unless plastic mountaineering boots are worn (and these are often uncomfortable for hiking, and frequently unnecessary for non-technical winter ascents), all too often when winter camping, boots are frozen solid overnight and can be quite painful to put back on in the morning. The alternative (to sleep with them to prevent them from freezing) is equally unpleasant, especially as I already put my water, gas and some clothing at the foot of my bag, so there's not a whole lot of spare room. Most of the moisture in the leather is the result of perspiration. If that sweat is eliminated, the result is a malleable boot, and much less of a wrestling match trying to don my footwear first thing in the morning!
Warmth and dryness are the primary rationales for vapor barrier (VB) socks and liners. A detailed account of how VB garments work, and their advantages and disadvantages, is unnecessary here. Suffice it to say that any item of VB clothing functions because it is essentially impermeable to moisture, and as a consequence the high relative humidity of the air trapped within the garment prevents a substantial amount of perspiration. With a normal sock, the evaporation of this sweat results in heat loss (added to which, wet body parts lose heat by conductivity far faster). VB clothing prevents this evaporation and the chilling which results. This is something of a simplification of a rather complex matter, but adequate for the purposes of this review.
RBH boot liners are constructed from a material that the firm has named VaprTherm. This is a textile laminate. The lining is black nylon, tricot weave (a smooth, light fabric); this provides a comfortable sensation against bare skin. This is bonded to a vapor barrier film, impermeable to moisture, and in turn this is covered with an insulating outer layer, what is described by RBH as "18 oz high performance fleece." The resulting composite feels fleece-like, but functions far differently from that fabric. The boot liners are not designed for use with socks underneath, but as a substitute for them, although I have worn thin synthetic liner socks on occasion without problems. In general, it's not a good idea to wear any clothing within a VB layer.
The claims that RBH makes for its VaprTherm technology are as follows (see website):
- Prevents degradation of insulation due to cumulative build-up of perspiration
- Blocks evaporative heat loss
- Keeps insulation dry and clean
- Adds up to fifteen degrees of warmth [i.e. a gain of 15 F/9 C]
- Helps prevent dry cracked skin
- Best protection against frostbite
Each liner is sewn from five panels of material (bottom, top, sides and rear), resulting in a circumferential seam around the foot, two seams on the front of the ankle and two on the rear. RBH claims that these are positioned in such a manner that they do not cause abrasion, and my experience is that this claim is valid. I have used the liners for hiking, skiing and snowshoeing and so far I have experienced no discomfort, let alone blisters. The top rim of each liner is serged to prevent fraying, and has a label with the name of the firm at the top rear of the ankle, as well as the VaprTherm trademark embroidered on the side.
The size seems to run true with my pair (a 13 or 13 1/2); however I sent the firm foot measurements that I had taken from a tracing along with my boot size. They prefer this procedure as it guarantees a better fit, and I would describe these as "made to order."
Laundry is entirely straightforward. They can be machine washed, and tumble-dried low. It's a good idea to turn them inside out before washing to remove skin particles.
Field Performance
In the past, I have generally hiked in winter wearing expedition weight Capilene socks (manufactured by Patagonia), though this year I experimented satisfactorily with my Dahlgren alpaca backpacking socks in moderate cold, as part of a BGT test. However, during January, February and early March I hiked and backpacked in the Adirondacks and Catskills (New York State) in temperatures that were on occasion fiercely chilly. The extreme occurred during an abortive attempt on the Seward Range in the 'Dacks. There, I experienced nighttime temperatures (outside the tent) of approximately -15 F (-26 C), with early morning temperatures that were not a great deal higher. Daytime temperatures at elevation were still pretty nippy, perhaps 15 F (-9 C). While these are hardly Arctic conditions, staying safely warm while base-camped or making ascents demands a certain level of preparedness and caution.
It was for these various adventures that I purchased the RBH boot liners. I wore these, at various times, with a pair of Scarpa Rios, a lightweight Asolo boot, and x-c ski boots. Neither the Scarpa nor the Asolo boots are insulated, although the former is (in my opinion) a superb, rather heavy boot for light mountaineering duty and the latter is a very comfortable boot for operating in milder, easier conditions (it's definitely a three-season boot). I was generally wearing snowshoes, skis or crampons, depending upon snow conditions. I was particularly concerned about the Rios freezing while I was camped, as they are made with a fairly heavy leather that would make them tedious, to say the least, to force on my feet if the boots were frozen.
I was very pleased with the performance of the liners, especially given the fact that I was "pushing the envelope" in regard to temperature with the boots I was wearing. As noted, neither are intended for severe cold-weather use, so as a back-up I had additional socks available at all times, a winter necessity in any case. Any accumulation of moisture in the leather over the day was minimal, leaving my boots nearly as supple and ice-free the following morning as when I took them off the night before.
I wore the liners for two days continuously at one point, as they kept my tootsies pleasantly toasty in my sleeping bag overnight. I found that my feet, which are sometimes slow to warm when I settle in to sleep, were quickly comfortable in the liners, and they stayed that way. Additionally, of course, they prevented my sleeping bag from absorbing sweat or odor from my feet (since perspiration trapped in the down can adversely affect its ability to insulate, this is a significant benefit). I'm not sure if continuous wear is by any means optimal for foot health, as fungi and other nasties like a humid environment, but I noted no ill effects and in fact my heels, which often crack, were improved at the end.
During the Seward trip in particular, my feet did feel a bit cold when I was inactive, for example when I was preparing breakfast or cooking dinner, but at no point was I so uncomfortable that I felt at risk, and a moment spent walking quickly eased any discomfort. I don't presently own a good pair of down booties, but based on past experience I would surmise that changing into these briefly in the morning and evening would have been helpful.
The claims made by the manufacturer for their product seem more than reasonable. Clearly evaporative heat loss was almost entirely blocked (yet at no time did my feet feel unpleasantly moist) and any accumulation of perspiration in my boots was forestalled. My feet never felt at any risk of frostbite (always reassuring!), and though I am hard put to quantify the "degree of warmth" gained, it actually felt like a good deal more than the RBH literature claimed.
I did not wear the liners at temperatures significantly over freezing. VB clothing can become very uncomfortable if worn at warmer temperatures, especially at high levels of exertion. While a VB shirt, for example, can be regulated to a degree by venting at the neck, these liners cannot.
Summary
The RBH boot liners proved valuable both by day and night for cold-weather backpacking. They provided a good deal of warmth at a minimal weight and prevented my boots from accumulating moisture from within. My feet warmed rapidly in my sleeping bag while wearing them, and stayed warm all night. They were also handy enough for day hikes, although the advantage over a good expedition weight sock is not as significant in this context.
Pro
- Liners minimize perspiration absorbed by boot
- Comfortable to wear for a protracted period
- A useful item as part of my sleep system, in addition to day use
Con
- Feet can feel a little cold when I'm stationary for a protracted period
