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Forty Below Light Energy TR Overboot and Simple Slipper SPOTLITE REVIEW

An extremely versatile and warm footwear system for snowshoeing and snow camping in frigid conditions.


Overall Rating: Recommended

The Forty Below Light Energy TR is more than an Overboot, its an integrated system consisting of the overboot, neoprene bootie (Simple Slipper), and camp bootie. This system is fairly lightweight and very durable, and works best for snowshoeing and snow camping in cold and frigid temperatures. It does not work quite as well in wet snow conditions because its neoprene fabric absorbs water, and seams and closures allow water to enter. We would love to see an ultralight version of the complete system, using lighter weight fabrics where possible and lighter weight insulation other than neoprene (which is fairly heavy).

About This Rating

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by Will Rietveld and Janet Reichl |


An overboot is an important component of a winter footwear system for snowshoe travel and winter camping in frigid temperatures. In our Lightweight Footwear Systems for Snow Travel project (to be published soon), we found the combination of the Forty Below Light Energy TR Overboot, Simple Slipper, and Camp Bootie to be the most versatile combination we tested. The “TR” stands for trail runner, and yes, this system is based on a lightweight mesh trail running shoe. How is it possible to wear a trail running shoe for cold temperature snow travel and snow camping?

Forty Below Light Energy TR Overboot and Simple Slipper SPOTLITE REVIEW - 1
The Forty Below Light Energy TR Overboot (left) weighs 17 ounces/pair and has a trim fit to wear over a trail running shoe or light insulated boot and moderate leg insulation. The Simple Slipper (right) is a 3-millimeter thick zippered neoprene bootie that weighs 9.8 ounces/pair. Weights are for overboots and booties to fit a size 12 shoe.

The TR Overboot is specifically designed for cold weather snow travel and snow camping. The foot section has a no-slip rubber dot outsole and 3 millimeter thick neoprene insulation with a durable ribbed nylon face. The gaiter section is uncoated stretch Cordura nylon on the sides and coated Cordura nylon on the back. It has a full-height 1-inch wide Velcro closure, with a snap and drawcord at the top. Inside, there is a removable 10-millimeter thick closed-cell foam insole to provide underfoot insulation.

The Simple Slipper is made of the same 3-millimeter neoprene as the TR Overboot foot section. The seams are glued and stitched for strength and water-resistance. It has a hefty YKK zipper that is not waterproof.

The Light Energy TR is more than an overboot, its part of a footwear system designed for extreme warmth, thus the name “Forty Below”. The system consists of the TR overboot (or one of Forty Below’s other overboot models), the Simple Slipper, and the Synthetic Fill Camp Bootie. The components can be worn separately, and when needed, all worn at the same time.

Forty Below Light Energy TR Overboot and Simple Slipper SPOTLITE REVIEW - 2
An efficient footwear system utilizing the Forty Below Light Energy TR Overboot and a trail running shoe would consist of (from left to right) a liner sock, heavy wool sock, mesh trail running shoe, Simple Slipper neoprene bootie, closed-cell foam underfoot insulation, and TR Overboot. In camp the Synthetic Fill Camp Bootie (far right) can be worn in the overboot, or the Simple Slipper plus the Camp Bootie worn in the overboot.

Forty Below Light Energy TR Overboot and Simple Slipper SPOTLITE REVIEW - 3
A footwear system for really cold temperatures utilizing the TR Overboot would substitute a light insulated boot (Kamik Force boot shown), 6-millimeter neoprene bootie (Crescent Moon bootie shown), in the TR Overboot. The TR Overboot has enough room inside to wear all of the components shown.

We did an immersion test at home to determine how water-resistant the TR Overboot and Simple Slipper are. We stuffed each with cotton T-shirts and a weight and immersed them in a pan of water up to their closure for an hour. The Simple Slipper did not wet through the fabric or seams to the inside, but the outside fabric absorbed quite a bit of water (1.8 ounces/bootie in the lower section below the zipper). We also observed that water readily leaked in through the zipper. The TR Overboot leaked a lot through the bottom seam and we found soaked T-shirts and standing water inside. The lower part of the overboot absorbed 2.6 ounces of water/overboot.

Forty Below Light Energy TR Overboot and Simple Slipper SPOTLITE REVIEW - 4
We tested the Forty Below Light Energy footwear system over two winters in a variety of conditions while snowshoeing and snow camping.

The Forty Below footwear system was designed for cold weather snowshoeing and snow camping, where temperatures stay well below freezing, and in those conditions this system really shines. Wearing the Simple Slipper inside the TR Overboot under those conditions, we had no moisture enter at all, and condensation was minimal in our socks and shoes. Our feet stayed warm all day, and it was easy to change socks at the end of the day and continue wearing the system, with the addition of the Synthetic Fill Camp Booties.

After snowshoeing all day in wet snow wearing the TR Overboot and Simple Slipper we found some dampness inside the overboot from water leaking in through the bottom seam, but it did not enter the Simple Slipper. This agrees with the results of our immersion test at home, and the amount of leakage in the field was less than we expected. Under higher exertion, we also found a fair amount of moisture from sweat accumulated in our socks. In camp, it was easy to change to dry socks, but the TR Overboot was too damp to wear our camp booties inside them. Rather, we wore a Tyvek bootie over our camp booties while drying out the overboots.

Since the neoprene fabric itself is mostly waterproof (specifically it doesn’t wet through, but the outside fabric absorbs water), we suggest gluing the bottom seam of the overboot and using a water-resistant zipper (like the Ri Ri AquaZip) instead of the Velcro closure to create a more water-resistant foot section of the overboot. Besides, we are not real fond of Velcro closures because the Velcro hook side can easily damage other fabrics.

Forty Below Light Energy TR Overboot and Simple Slipper SPOTLITE REVIEW - 5
We found the TR Overboot and Simple Slipper to be sufficiently durable to handle the abrasion of snowshoe bindings and rivets. The sole of the overboot is a durable rubber dot material that does not slip on snow, and the neoprene in the foot section of the overboot and Simple Slipper has a ribbed nylon face fabric that is also very durable.

Since the Simple Slippers did not leak through in our immersion test, we tried snowshoeing in them with a gaiter to keep snow from entering through the top. That system was very lightweight and kept our feet warm and dry in dry snow (as long as we kept moving), but in wet snow the booties absorbed quite a bit of water in their outer fabric and leaked some through the coarse zipper.

Forty Below Light Energy TR Overboot and Simple Slipper SPOTLITE REVIEW - 6
(Left photo) The Simple Slipper neoprene bootie and a gaiter can be worn over a trail runner for snowshoeing in dryer snow, but not in wet snow. (Right photo) In extreme cold on the trail or in camp, a trail running shoe and Simple Slipper can be worn inside the Forty Below Synthetic Fill Camp Bootie and TR overboot for extra warmth.

Overall, we were very pleased with the performance and versatility of the Forty Below Light Energy Overboot and Simple Slipper, separately or in combination. It is especially suited for cold and frigid conditions where there is no liquid water to enter through the seams or closures. The Forty Below three-part system (overboot, neoprene bootie, and camp bootie) is all that is needed (except perhaps vapor barrier socks in extremely cold conditions) to keep feet warm and dry while spending days out in the snow.

Actually, the Light Energy TR Overboot is just the first of a suite of new lightweight overboots that Forty Below will offer. All will have a non-slip rubber dot outsole, breathable stretch Cordura on the sides, waterproof Cordura on the back to shed snow, a full-length Velcro closure, and a removable closed-cell foam insert.

The MT model designed for mountaineering will be coming in summer 2007. It will be sized for mountaineering boots in the foot section and heavier insulation in the leg section, and will have reinforcements in the toe and heel areas to accommodate a range of step-in crampon bindings.

The SL model, arriving in winter 2007, will be a shell overboot with no built-in insulation. The estimated weight is 6-9 ounces/pair. It will have a trimmer fit for trail running shoes like the TR model, and will also accommodate the Simple Slipper and Synthetic Fill Camp Bootie to provide a complete footwear system for snowshoeing and snow camping.

The Forty Below XC model will also come out in winter 2007 and will be designed for use with backcountry ski boots, including the ability to accommodate different XC bindings.

Features and Specifications

  • Manufacturer: Forty Below (
  • Sizes: XS-XXL to fit from women’s 4 to men’s 16, plus custom sizes available on request (the new overboots will be made upon order, which will require about 4-6 weeks for delivery)
  • Insulation: 3 millimeter nylon-faced neoprene foam
  • Fabric: TR Overboot sole is rubber dot material, sides are stretch uncoated Cordura nylon, back is coated Cordura nylon; Simple Slippers are 3 mm nylon covered neoprene foam
  • Features: TR Overboot has a non-slip sole, insulated foot section, durable Cordura nylon gaiter section, full-height 1 inch wide Velcro closure, snap and drawcord at the top, removable 10 mm thick closed-cell foam inserts; Simple Slippers have glued/stitched seams and a heavy duty YKK zipper
  • Weight: Measured weight of the TR Overboot in size XL is 17 oz/pair (482 g); manufacturer specification 16 oz/pair (454 g) for size Large; measured weight of the Simple Slipper in size XL is 9.8 oz/pair (278 g), manufacturer specification 8 oz/pair (227 g) for size Large
  • MSRP: Light Energy TR Overboot $129.95, Simple Slipper $59.95


"Forty Below Light Energy TR Overboot and Simple Slipper SPOTLITE REVIEW," by Will Rietveld and Janet Reichl. (ISSN 1537-0364)., 2007-03-25 03:00:00-06.