I’ve had the ATC Short Sleeve Half-zipped base layer for a while, almost as long as the garments title.
For a while it has been a regular runner and one which I’ve never had any irrigation, chaffing or destroyed nipples. Thank fully, the latter is something I’ve yet to experience and long may that continue!
The title of the top is pretty is self explanatory – Short Sleeve/the sleeves are short, Half-Zippered/stops at the base of your sternum & base layer/next to skin. It may not roll of the tongue, but you can’t accuse inov-8 on misleading or confusing you.
So where have I been using it I hear you ask?
In the rear of the above photo are my local trails. A mixture of flat woodland, sand and mud, that forms the basis of most trail training runs. The highest point is a staggering 133ft, and feet is what I shall call it, as the meters equivalent is even more pitiful.
I’ve spent many evenings and mornings, dodging dog walkers, horses and mountain bikers wearing the ATC SSHZBL. Now despite what I thought the first time I put on the half zip, I do use the zip more often than many may imagine. I run hot, and enjoy the extra ventilation it provides, with the ability to quickly zip it shut, should an ice cool breeze come in my path. I’ve worn it on the fells of the Lake District, the Grand Col Ferret at UTMB and on the slopes of Ben Nevis, amongst many other exploits in the mountains.
The length is good. I’m 5ft 7″ and most products in a medium can often be well over my bottom… and when your legs are as short as mine, that can lead to looking like a dress. Not the case for the ATC SSHZBL, perfect length and the arms also offer good cover/sun protection. 
The rear,sides and under arm are well ventilated, much like a road cycling gilet and this really does let air out. I run hot, sweat a lot and this is noticeable. On the neck, there is also an inner rucksack band, designed to keep your pack at bay. It works. Some may think unnecessary, but if you have a larger pack brimming this does form a comfort layer and barrier. 
As much I as a fan of the comfort of the SSHZBL, for me it comes a price. That same material which aids to the durability (mine looks new some 12 months on) also runs a little warm. In the heat of summer, I tend not to use it, as I do find I run hotter than in lighter weight options out there. This of course is very much personal preference, as you’ll see me in the middle of winter in shorts and t-shirt…. With cooler temperatures on their way, it is back out on the trails and I’m enjoying reuniting one step at a time. 
Reflective details on the left chest, arm and neck provide good visibility at night and the Polygiene permanent anti microbial treatment does stop the top from humming after long warm sessions. Trust me, my partners the first to say if I stink if not. Just think of the Lynx man, she’s a lucky lady…..
So, the inov-8 ATC Short Sleeve Half – Zipped Base Layer doesn’t smell, has good ventilation, visibility and stands up well. I may find it runs a little warmer than I’d like, but that is the only grumble I can find.
Now, one catch. It’s discontinued. However you can still get it from inov-8 in smaller sizes HERE.
For those shouting at their screen “James, why did you not tell us sooner??” all is not lost.
inov-8 have recently launched a new range of running tops, along with jackets and accessories for this winter.
Having got hands on with the new Short Sleeve Base Layer and Long Sleeve Base Layer I can confirm they are lighter, feel softer and should be as they state, more breathable. And if proof is required of how long their kit can last, the shorts in the photo were bought by me more than 5 year ago and still going strong.
James Mackeddie 
I use the AT/C merino base layers on my bike under a windshell if it isn’t raining and they’re great – got both short and long sleeve ones, lovely and thin – and easy to layer. When it’s cool, wet & sweatier I go for Craft baselayers under a waterproof as they’re just the best fitting and most effective wicking layers I’ve found in the last 6 years, with no constriction at all. They’re not as warm as merino, but that’s often a good thing when you’re working hard, no matter how “breatheable” your waterproof claims to be.
Love the Inov-8 AT/C tank too – would be great to see it back again in more colours.
Inov-8 do some really great kit and being your height but a lot slimmer I usually fit XS best, which hardly anyone offers – or when they do the armpits are cut too high or the tops are finished too short at the hips. Of all the gear they offer I didn’t get on very well with the half-zip in a smaller size because although it’s finished with a zip guard the neckline was just a little too high and tight for comfort. Not something that was an issue with zip-less baselayers.
In the main though, Inov-8 are saviours when it comes to enjoying the rare luxury of proper fitting sports clothing which doesn’t flap for people of my build – and I’m a huge fan. The only problem is very few stores stock a full size range, even less so this year, and deals are much harder to find if you’re an XS. So I have to buy less and look after what I have more carefully. Thankfully for the most part quality is very good so stuff does last, it just means more frequent washing !
After trying at least 10 mid-layer longsleeve tops this year from various bigger brands (including Nike and Adidas) I came back to this one from the A/W Inov-8 range, which I can definitely recommend for anyone looking at options – looks great, feels great, top quality and fits like a dream : https://www.inov-8.com/men/clothing/mid-layers/long-sleeve-half-zip-mid-layer-mens-red .. the zip guard is fantastic (something all the others I tried really didn’t get right) and, exceptionally, it’s a perfect length.
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