The Grettir top from Icelandic brand 66North is a versatile and lightweight mid-layer that works best on cooler runs

Icelandic folk know a thing or two about kitting up correctly for changing conditions. Outdoor kit maker from that Atlantic island, 66North, specialises in making gear built to handle much more than your daily 5km plod, like this Grettir Long Sleeve running top.  

Men’s Fitness verdict

The Grettir is an ideal insulating mid-layer that works surprisingly well for such a lightweight top. We found it’s best worn over a base layer though flatlock seams guarded well against chafing.
  • Light and quick drying
  • Chafe-beating flatlock seams
  • No thumb loops
  • Somewhat expensive

How we test running tops

Kieran Alger is a running fanatic and professional run-tester. He tested this running top, as well as those featured in our buyer’s guide, over a wide range of distances, terrains and even countries. One test took him to an Italian ultramarathon; while others were conducted on the towpaths of West London, where he lives.

The Grettir’s half-zip design is useful for controlling ventilation

66North Grettir Long Sleave Top design

This multi-purpose, super-light Grettir long sleeve top takes all that climate control expertise and packs it into a zippered layer that brings lightweight warmth to colder runs. But it’s not just for running; this top has excellent multi-sport versatility too. You can use it for everything from plodding and hiking to cycling and climbing.  

It’s made from Polartec Power Dry, a blend of polyester and Spandex that’s thin, minimal and highly breathable. It’s quite hugging and snug so you might want to buy a size up if you like your tops looser. But in my tests the fabric felt soft and cosy against my skin and it flexed nicely. Even if the fit is snug, it’s not restrictive. 

Details like flatlock stitching helps cut the risk of unwanted seam rub. However, this top is quite textured on the inside and that could present some added chafe risk if you wear it on its own.   

Lightweight performance

In my tests, it worked best as a mid-layer over a thin base layer for cooler autumn and winter runs. You can wear it on its own under a jacket – though you may want to lube your nipples on long runs. However, the fact it’s so thin, light and fast-drying means it never suffers from nipple-bothering heavy sag.  

It’s light enough to stash in an ultra running vest and the half-zipper design makes it easy to get on and off – which is great for boosting your warmth mid-run, or having as an extra layer post-run.  

My only other quibble is that I would have liked some thumb loops to help keep the sleeves in place. 

The 66North Grettir comes in six sizes from small to 3XL, has to be washed cold and can’t be tumble dried. I also like the fact that it comes with repairs for life.