The North Face Isotherm 1/2 Zip Review

The following review was included in Issue 10, Autumn/Winter 2013 of Barefoot Running Magazine.

The North Face Isotherm ½ Zip Shirt arrived with me just in time for the drop in temperatures that heralded the end of a brilliant summer and, since that point, it has been in constant rotation, having been worn not just for running but for anything and everything from hiking and biking to general everyday use.

The Isotherm, billed as “an innovative hybrid trail running top designed for protection and warmth,” is available in both men’s and women’s styles and is definitely worth a look if you are considering what to wear to see you through the Autumn and Winter months.

When it comes to the worst of the Autumn/Winter weather, most notably the snow and rain, the Isotherm will be paired up with a breathable waterproof layer to add that additional element of protection. At the time of writing I haven’t yet had the opportunity to test the Isotherm in extreme cold but, from the forecast, it would appear that I will not have to wait too long to be able to do this!


The Isotherm ½ Zip Shirt comes in Nautical Blue/Estate Blue or TNF Black/Asphalt Grey colour combinations.


The Isotherm offers a really comfortable fit, neither overly large nor overly tight. My standard XL size provided the perfect fit and it was as comfortable sitting at a desk as it was out on the trail. The only potential issue would be with regard to the sleeves which, with their built in mitt protection, are slightly longer than standard sleeves. However, the mitt element can easily be folded up into the sleeve.

Build Quality

As you would expect from The North Face, the quality of the garment is excellent, well constructed with neatly stitched seams and good attention to detail. Despite repeated washes over the short time that I have had the Isotherm, it shows no sign of degradation at all.

The Isotherm uses proprietary fabrics developed by North Face, including FlashDry™, which incorporates microporous particles to improve moisture management and temperature regulation during outdoor activity. FlashDry™, used across a wide number of products in The North Face range, accelerates the removal of moisture from the skin, enabling the user to stay drier and more comfortable for longer. FlashDry™ is permanently embedded in the yarn and won’t wash out.


The Isotherm ½ Zip is part of The North Face’s Flight Series running collection, athlete tested and competition proven, and, as such, you have high expectations for the garment.

The Isotherm consists of a wind resistant core which blocks the wind and helps to retain heat, with a wool blend on the sleeves and FlashDry™ paneling for ventilation on the sides of the garment, down the back, and under the arms.

The built in sleeve mitts can be folded up inside the sleeve or simply rolled up around the wrists when not in use. However, chances are you are going to want to make use of the hand protection afforded by these, especially in the chillier temperatures. They are no substitute for gloves in really cold temperatures but are certainly useful on those days when gloves would be overkill and result in overly hot hands.

The double zip used in the ½ zip neck is one area where the attention to detail is evident. I actually overlooked this feature at first, not appreciating just how useful the double zip could be. It facilitates optimum control over ventilation, enabling full coverage when zipped up, ample ventilation when zipped down, or a combination approach if the bottom zip is used. Zipping up from the bottom permits easy ventilation of the chest area without the need to leave the neck flapping around, a useful feature for those days when the winter sun heats you up.

The neck of the garment has a cover to prevent the zip from rubbing against your skin.

There’s a useful zipped chest pocket that’s perfect for holding a key or a lightweight MP3 player.

360 degree reflectivity is provided as a result of reflective logos and use of reflective trims, with the traditional The North Face logo on the front, and a Flight Series logo on the rear of the garment.

I was initially quite surprised at the combination of materials on the Isotherm. The shiny core seemed at odds with the wool blend sleeves and FlashDry™ paneling. However, having tested the Isotherm in a variety of scenarios, I can see how well the separate elements work to provide the perfect conditions for running.


RRP £85.00

Overall Rating

The Isotherm ½ Zip Shirt certainly ticks all the boxes if you are looking for a top that offers wind resistance, temperature regulation, breathability and comfort. It’s the quality product that you would expect to come from The North Face and the combination of a wind resistant core and FlashDry™ paneling results in a garment that doesn’t leave you chilling in your own sweat. The double zip and built in mitts are useful additions to the garment, adding to the overall functionality. Definitely a garment worthy of consideration if you are looking for something to see you through the colder months.



  • Two-way zip
  • Reflectivity at zip
  • Shaped hem
  • Thumbholes
  • Secure chest pocket
  • Reflective logo
  • Fabric
  • body: 200 g/m2 56% merino wool, 37% polyolefin, 7% polyester knit
  • panel: 76 g/m2 100% polyester woven