Welcome! Ultralight backpacking is my passion, and keeping up on new technologies, gear, and techniques relevant to UL backpacking is what floats my boat. I'm always looking for the lightest, most functional gear to improve a lightweight or ultralight backpacking kit, and report my impressions and field testing results here. For hikers wanting to keep up on the latest and greatest ultralight backpacking gear, this is a good place to hang out. Also, there is a lot of information here (and on our informational website Southwest Ultralight Backpacking) on useful techniques and backcountry etiquette -- food for thought for hikers wanting to lighten their load and their impacts.

My goal for Ultralight Insights is to understand, test, and report on new technologies and gear of interest to lightweight and ultralight backpackers. It's a passion after all, so we just plain enjoy talking about it. I hope readers will add their own wisdom and comments, respond to my questions, ask their own questions, and correct me if I get something wrong. Happy hiking! Will

Saturday, January 30, 2016

GEAR REVIEW and My Favorite Gear #7: Seirus Heatwave Glove Liners, Skull Liner, Socks, and Zenith Mitts

By Will Rietveld

The Seirus Heatwave technology is described as “a dual-stage heating system involving: 1) a kinetic stage that amplifies temperature 4-5 degrees, and 2) a reflective stage that returns 20% more warmth”. The “kinetic stage” is a bit hard to understand; I believe it means the black outside fabric absorbs infrared radiation and transfers it inside. The reflective metallic lining inside the garment is easy to understand; it reflects heat back to your skin. We have seen something similar from Columbia, who added a reflective lining to jackets and sleeping bags.

I was attracted to the liners for ultralight backpacking because they are very lightweight in addition to being reflective for extra warmth. The lightweight insulated Zenith Mitts, with a waterproof/breathable membrane, are potentially a good choice for snow sports.

Features and Specifications

Seirus (www.seirus.com)
Heatwave Glove Liners, Socks, Skull Liner, and Zenith Mitts
No fabric description is provided for liners; Zenith Mitt shell is taslan with a SureGrip palm
Measured Weight
Glove Liner 1.15 oz/pr, Socks 1.95 oz/pr, Skull Liner 0.85 oz, Zenith Mitts 6.2 oz/pr
Glove Liner $20, Socks $35, Skull Liner $25, Zenith Mitts $50

Seirus Heatwave Glove Liners

The liners I received for review are a bit strange; as sewn, the reflective layer is on the outside, which doesn’t make any sense to me. Seems like it should be on the inside to reflect heat back to your skin. When asked if that was a manufacturing error, the company representative reported back that they are intended to be that way. I still don’t understand why the glove liners are different from the Socks and Skull Liner, which have the reflective layer on the inside. I have seen other people wearing the Glove Liners with the reflective layer on the outside, so the liners I have are not unique. If someone can explain this to me I would appreciate it. I tested the Glove Liners inside out (with the reflective layer inside) because that makes sense to me.

The Seirus Heatwave Glove Liners have the reflective layer on the outside, which differs from the illustration above and the other Heatwave items tested.

Besides their light weight (only 1.15 oz/pr in size L/XL), the glove liners have a 4-way stretch which allows them to form fit my XL hands.

I took the Glove Liners on several summer backpacking trips in the Southwestern Colorado Mountains, usually camping above treeline where nighttime temperatures can drop into the 30s F. Wearing the liners in camp and occasionally on the trail, I found them to be comfortably warm when dry. However, they are not water-resistant at all, so when they get damp or wet they are definitely cold, as one would expect. After using them on several trips they show no signs of wear. I did not wear them while bushwhacking, which I doubt they could withstand for long.

Coincidentally as I write this review, I went on a snowshoeing trip with a group of friends, and two others in the group were wearing the Seirus Heatwave Liner Gloves. They wore them with the reflective layer out, and look what happened to them in this photo -- after only two months of use in this case the reflective layer showed considerable wear, especially where they were in contact with trekking/ski poles. This is another reason why it doesn't make sense to sew the liners with the reflective layer on the outside.

Overall, I found the Seirus Heatwave Glove Liners to be a good choice for ultralight backpacking. They weigh about the same as a pair of thin wool glove liners, and (in my opinion) are an increment warmer, as long as they are kept dry.

Seirus Heatwave Socks

I got the Heatwave Socks in size Large, which fits men’s sizes 9 to 11.5. My size 12 feet are a bit beyond that range, but the socks fit perfectly. The seams are designed so the socks anatomically fit my feet very well, and have flat seam construction with reinforced stitching so they are comfortable to wear and long-lasting. They are tall, 14 inches from heel to hem. Unlike the glove liners, the Heatwave Socks have the reflective lining on the inside (where it belongs, in my opinion).

Seirus Heatwave Socks

For a mere 1.95 ounces, the Heatwave Socks provide a lot of warmth for their weight, as I discovered on several summer backpacking trips in the mountains. An ultralight camp footwear system I use is a thin plastic bag over my foot, then the Heatwave Socks, then a Tyvek bootie. The total weight is 1.4 ounces/foot. This keeps the socks dry and my feet warm in camp and in my sleeping bag.

The Heatwave Socks can also be worn as a liner inside other socks, or inside waterproof/breathable socks. My favorites are the Rocky Gore-Tex socks. I did not test these alternative uses.

Overall, the Heatwave Socks are another winner; they make excellent ultralight camp and sleeping socks. They have been worn and laundered a number of times and are still in like-new condition.

Seirus Heatwave Skull Liner

This is otherwise known as a skull cap or a helmet liner. With its Heatwave lining on the inside, the Skull Liner is surprisingly warm under a hiking cap on the trail when a cold wind blows, and as a camp hat while mountain backpacking. It covers my ears (barely), which mostly eliminates wind roar in my ears when hiking in wind. As a sleeping hat it is sufficiently warm in a mummy bag with an insulated hood, but it’s a bit on the light side for sleeping in a hoodless bag or quilt in temperatures below about 40F.

Seirus Heatwave Skull Liner.

It comes in one size and stretches to fit. It weighs only 0.85 ounce, about the same as a thin fleece skull cap, so it too finds its way into my ultralight gear kit.

Heatwave Zenith Mitts

The Zenith Mitts are a different product for a different purpose. They are insulated, windproof, waterproof /breathable mitts intended for snow sports and general cold weather handwear. The exterior fabric is a soft taslan and the SureGrip palm is soft, grippy, and durable. They have the same reflective lining as the liners reviewed above. Insulation is 250-gram HeatLock and the membrane is called DryHand. There is a small gauntlet on the wrist opening with a one-handed cinch closure.

Seirus Heatwave Zenith Mitts

I tested the Zenith Mitt on several winter backcountry skiing and snowshoeing trips, by themselves and inside a shell mitt.

The mitts fit my XL hands well and my initial impression is they are very soft and warm.

However, after wearing them several times I realized their limitations. I found them to be suitable for moderately cold conditions (20s F), but chilly to cold below that. When moisture from sweat builds up inside the mitts they are less warm and the lining has a lot of resistance to pulling my hands out and putting them back in.

The mitts’ gauntlets are a bit of a conundrum; they are too bulky to fit inside the cuff of a shell jacket, but the mitt opening is not large enough to fit over the cuff of a shell jacket. The result is the cuffs butt together, allowing snow to get in.

When I wore the mitts in snowy weather they got wet and I suspected they were leaking. So I tested their waterproofness at home by immersing a mitt in a bucket of water down to an elastic binding just below the gauntlet. After 1 hour I checked the mitt for leakage to the inside, and found it to be dry inside. Good so far. However, the exterior fabrics, and perhaps the insulation, absorbed a great deal of water. The dry weight of the mitt was 3.15 ounces and the wet weight was 7.75 ounces, so the mitt absorbed 4.6 ounces of water! That’s more than double the initial weight. These mitts have a waterproof/breathable membrane, but the mitts themselves are not waterproof; they soak up water like a sponge!

From my test results I recommend that the Zenith Mitt be worn by itself only in dry weather (where it will breathe better), or worn inside a waterproof shell in wet weather (which will keep the mitt dry, but will seal in perspiration).


The Heatwave Glove Liners, Socks, and Skull Liner are a good find for an ultralight backpacking kit. They are very lightweight and functional, just what we are looking for, so they land on my favorite gear list.

However the Heatwave Zenith Mitts have some caveats: they are only moderately warm (warmer if you wear a shell over them), and it’s important to keep them dry. The exterior fabric (everything exterior of the membrane) is very absorbent, so the mitts easily soak up water resulting in cold hands.


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