45Nrth Jaztronaut Insole Review

It doesn’t take a cyclist to know that the first two things that typically get cold are the hands and the feet. Based out of Minnesota, 45Nrth is a brand dedicated to creating products for cold weather cyclists who brave the rough elements. With the introduction of their Wolvhammer winter boot also came the introduction of the Jaztronaut insole. During the design process of the Wolvhammer boot, 45Nrth developed an insole solely for the purpose of keeping your feet warm. Once they realized just how well the new insole worked, it was released as a unique product in addition to the boot, packaged for all to enjoy.

After having ridden these in all sorts of temperatures, they have become a welcome addition to my winter gear.

Features and Design

Aerogel laminated between two layers of foam and topped with a light fleece for a soft touch.

The Jaztronaut is based on aerogel, a lightweight class of materials that was developed in 1931. Today, it’s used by the likes of NASA for spaces-suits and beyond. Aerogels make up the world’s lightest solid materials and are comprised of 99.98% air. Additionally, aerogel makes a perfect material for cycling insoles: it can be made with high resistance to compression, supporting more than 1,000 times its own weight.

Construction of the insole is fairly simple. It has two layers of EVA foam sandwiching a 2mm layer of aerogel in between, all topped with a light, soft fleece. The lower EVA layer is more rigid to provide durability, while the upper EVA layer is a softer compound for comfort.

The insoles come in a range of sizes, and the smaller sizes will need to be cut down to the appropriate length. It must be noted that you don’t want to cut beyond the white line indicated. Cutting too close can expose the aerogel layer, which may cause skin irritation. Any cutting beyond this line will also void the warranty.

Cutting to Size and Inserting

Sharp, quality scissors are necessary for a good clean cut.

After taking the insoles out of the package, I was underwhelmed. They seemed to run narrow and they looked pretty standard, particularly in contrast with the arch support and and cupped heel on my existing insole. At first glance, they did seem to run true to size — close enough to perfect that I just jammed them in my shoe with no preparations, giving it the good ol’ trial and error test.

After cramming them into the shoe, it was evident that I needed to cut them as indicated. Grabbing a quality pair of sharp scissors, I cut along the white line. To do this, you’ll want to use the sharpest pair of quality scissors you have or can find. I suspect a dull pair will struggle and bind up under the thickness of the materials. Once they were cut, they fit in the shoes really well.

Fit, Feel and Performance

In our case, the thin design fit well, but we needed to readjust the straps on our shoes for a proper fit.

With the new insoles ready to go, I stuffed in my foot, wearing light-to-midweight winter socks. Surprisingly, they were indeed thicker than my stock insoles, creating a tighter fit than I was going to be able to ride with. I loosened the straps and readjusted them to accommodate the extra room needed. Since my shoes are weathered, worn and broken in after many seasons, they didn’t like to be widened and took a few rides to fully settle into a new shape. Even though it’s a flat insole, the feel right out of the package is not bad at all.

Here’s where this understated product starts to come to life. The day I tested the insoles, my office space and its concrete floor were particularly chilly, and so were my feet. But within seconds of putting on the Jaztronauted shoe, I began to feel heat radiating from under my heel. I was taken aback and rushed to try on the other shoe. Same result. At this point I wanted to make sure I wasn’t losing it, so I pulled them out and tossed them over to our graphic designer so that he could give them a test in his shoes. To my relief, he confirmed the same thing — they reflected the warmth back up almost immediately.

Since putting them in my shoe, I’ve ridden nearly 200 miles in temperatures ranging from 6-35F. I’ve done multiple rides over an hour and a half along with daily, 25-minute commutes to work. Since putting these in, my feet have been happy and mostly toasty. I haven’t run into any issues with breathability, especially when paired with socks that do a good job of wicking moisture. They work very well, cutting off cold from the shoe’s bottom where cleat plates typically spike a chill.


45Nrth Jaztronaut Insole

There are a few drawbacks to these insoles. As mentioned earlier, there is the fit issue when it comes to standard riding shoes. This is to be expected with just about any insole or even sock. Because of the tight, snug fit of cycling shoes, even a heavy sock can be a problem when it comes to fitting a shoe that you wear all summer with a lightweight sock. For myself, this was something I was able to overcome.

While the bottom-up warmth performs beyond expectations, keep in mind that it’s not a total solution for foot comfort. You’ll still need some sort of shoe cover to keep the wind and cold from penetrating the ventilation on the top side. This is to be expected, of course, as these are two separate areas of the shoe.

The last drawback is that this product is designed to fit as many people as possible, but can’t fit them all perfectly. Because of the cut-to-size design and the need to seal the aerogel inside the layers by laminating them, it leaves a ring around the edge that doesn’t have Aerogel in it. This isn’t an issue at the heel, mid and ball of the foot, but I noticed that my toes overshot the aerogel portion, growing a little colder than the rest of my foot. I would suspect that if you fall within the larger of the doubled size range and forego cutting down, you’ll find more material up front without aerogel in it.


These things perform better than I could have hoped. At $50, I find them to be a great value to update your existing gear for more rugged, cold weather conditions. While not a perfect design, it is worth noting that they were designed for use in the Wolvhammer boot and repurpose traditional shoe use. So far, they’ve improved my cycling experience this winter and left me whining about my hands as the last remaining cold extremity.

Despite the drawbacks, they are worth considering because they simply work. It’s a product that I’m glad I’ve purchased and have no regrets now that I’ve worked out all the kinks.

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