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Forty Below K2 Superlight Overboots Review

Forty Below K2 Superlight Overboot



The Forty Below® K2 Superlight™ overboot is an insulated boot cover designed for high altitude and cold weather climbing. They provide additional warmth in extreme conditions and extend the temperature range of single leather boots.

Approximate Price: $159.00 USD

Use: Technical Mountaineering in extreme cold

Colours: Black, Red

Size: (length of boot sole) XS 10.75-11", SM 11.25-12.5 MD "11.50-12", LG 12.25-12.5", XL 12.50-13.5", XXL 13.5-14"

Weight: 1lb 5 oz (588g) per pair size medium

Material: 4.7 mm stretchy closed cell neoprene foam insulation, with 2 layers of heat reflecting Titanium

Crampons Compatibility: Step-in, New-matic, Strap-on and Wire toe bail style ski mountaineering bindings.

Uppers: Non-coated, windproof and breathable Cordura nylon

Outsoles: This coating of rubber paint

Forty Below K2 Superlight Overboots on Orizaba


I recently had the opportunity to test the K2 Superlight Overboot from Forty Below. Overboots differ from supergaiters in that they also cover the sole of the boot, enveloping the entire foot. Because they cover the bottom of the boot you must wear either crampons or snowshoes at all times, thus limiting their usable range to snow or ice conditions where the rock is easy enough to use crampons.

Because they must be used in snowy conditions, I tested them during a winter ascent of the glacier of Pico de Orizaba and mixed ice climbing on frozen waterfalls in the Montreal River area of Northern Ontario.

Initial Impressions

Initially I was skeptical. The ankle high insulation looked inadequately thin and the knee high gaiter appeared flimsy. They certainly folded down into a small package though - a huge plus for pack weight.

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They are sized by length and my size 42 Scarpa Triolet Pro GTX boot equated to a Medium. Forty Below states that they're intended for a double plastic boot but will also work on single leathers. The added space required for the plastics was apparent as the fabric seemed to bunch up under the straps. They seemed to be slightly too wide for my boots. This worried me because kicking the neoprene with a crampon would easily tear it.

Otherwise, the length was near perfect and they slide on with relative ease. Some wiggling was required to seat them perfectly and I wouldn't want to be doing that with cold fingers. I used Petzl Vasek crampons with a lever lock. The crampons did not require any adjustments and locked securely in place. I was very pleased with how easily this was accomplished.

I didn't immediately notice my feet being warmer or anything. The felt as though they would breathe well and it didn't feel like wearing a plastic bag. I also tried wearing only the overboot without the mountaineering boot inside as a camp bootie. Although it was obviously far too large it was quite cozy and i felt well protected from drafts of cold air or chilly floors. They were a nice change of pace around camp after a long day of climbing.

Glacial Travel

I was able to wear my three season boots up Orizaba in March to the base of the glacier and the overboot was relatively simple to put on under the illumination of my headtorch. After a few hours up to the summit and down I hardly noticed them at all as they were barely more intrusive than a gaiter. The temperatures ranged from -5 to +5 degrees Celsius and the combination was perfect for these conditions. I did stumble once as the front point of my crampon caught the fabric but it was not detrimental. I was very pleased with their performance.

Ice Climbing

To gauge their suitability for ice climbing I fit them to a size 9 double plastic Scarpa boot for mixed climbing on northern Ontario waterfalls. The added width of the double plastic fit much better but, as a tradeoff, was much harder to put on. It was still manageable. Once again I nearly forgot I was wearing them as they did not affect my climbing in anyway. However, this was during the recent Polar Vortex where conditions dropped to -25C and the combination was simply too cold to make the activity enjoyable. A few degrees warmer and it would have been suitable.


As expected, the slight oversizing resulted in loose fabric which was promptly kicked while clambering over awkward terrain. The damage minimal with a few minor tears in the upper fabric (which could easily be sewn or patched) and one small tear in the neoprene which was fixed without any difficulty using the provided repair kit.

These overboots really shine as a "boot season extender," enabling me to wear three season mountaineering boots in warmer winter conditions. I will state, however, that the ultimate underlying factor is the warmth component of your choice of boot. I'd estimate the this product extended the wearable range by approximately 10 degrees Celsius so don't put a pair of these over a summer hiking boot and try Denali. Although if you're wearing appropriately insulated boots for your conditions and want the added peace of mind or you're prone to cold feet, this is a fantastic addition to your alpine apparel tool kit.

The customer service I received from Joel at 40 Below was exemplary. He was very helpful and ensured my product was shipped to me in a timely fashion. I was very impressed.

This product did exactly what it claims to. It delivers an extra layer of warmth and extends the wearability of your expensive mountaineering boots. They fold down small and store easily in your back and essentially provide you with two different boots for different alpine conditions. These now accompany me on all winter climbs and I would recommend this product to all mountaineers.

K2 Superlight Rating

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The purpose of my reviews is to offer the reading audience an objective opinion, so they can make an informed decision before buying.

All my reviews, opinions, and everything expressed here are my own and based on my experience with a product. I am not affiliated with any of the brands mentioned on my blog nor do I endorse them and they do not endorse me. I am not paid for my reviews. Occasionally, I am provided free products for review, in which case I will make that abundantly clear. Anything discussed on this site is expressed as my own opinion and I reserve the right to my own opinion when discussing my experiences, products, or anything else.

Mountaineering is inherently dangerous. Any information provided is for informational purposes only and should not be used as a replacement for advice by a trained professional. Please ensure you're climbing within your skill level and receive appropriate training before embarking on any potentially dangerous activities.

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