Haglöfs L.I.M. ZT II Air Base Layer review: a peak-performance undergarment

First impressions

Although it only comes in one color, the ZT II Air Base Layer top from Swedish outdoor gurus Haglöfs has a funky dot-pattern design that instantly makes it look satisfyingly technical. Design-wise it seems like a pretty standard, albeit good-quality long-sleeved base layer, but there is a bit more going on here than meets the eye.

The material mix, design and cut of the top all contribute to enhanced comfort and performance levels, especially when it’s paired with other pieces of alpine-orientated apparel in the Haglöfs’ new L.I.M. ZT II range.

It also has a splash of style, and can be worn as a stand-alone top in dry, warmish weather, when you still require a little bit of cover from the elements. With small reflective flourishes on each shoulder and a large neon yellow section on the back, the top makes you nice and visible on roads and tracks shared with vehicles.

Fabrics & design

A base layer might not seem like the most glamorous piece of kit, but as the garment upon which everything else is built, it’s extremely important. Wearing the right base will make a big difference to the enjoyment levels of any given escapade you set off on, but especially those that venture skywards, into the mountains.

The first job of a base layer is to provide a level of thermal protection, but if it’s itchy or uncomfortable, or if it fails to let your body breathe or adequately wick your hard-earned sweat away when you’re exerting yourself in the great outdoor alpine gym, you are not going to have a fun time.

Fortunately, the Haglöfs L.I.M. ZT II Air Base top does everything asked of it, with aplomb, and made with a thin and ‘cooling’ 115g/m2 knitted Polartec Delta fabric, it feels luxuriously lovely to wear. The material mix is half lyocell (an eco-sensitive plant-based fiber) and half recycled polyester, with a little bit of elastane thrown in to provide some dynamic stretch.

L.I.M. stands for ‘less is more’, and the signature element of everything in this range is that it starts off weighing very little, and remains light even if you sweat profusely or get caught out in the rain. Accordingly, the Polartec Delta fabric features both hydrophilic fibers (to draw moisture away from the body) and hydrophobic fibres to make sure it evaporates quickly.

Perfectly panelled to permit a good range of movement, the top is finished off with flat seams, to avoid any rubbing issues. The design is reasonably standard for a long-sleeved undergarment, but there are good features that make this top stand out, and mean than it can be worn with or without other layers, including reflective details, a nice crew neck, a hang cord and thumb loops on each cuff (something I really like to see on base layers).

On the trails and in the hills

I have been testing the Haglöfs L.I.M. ZT II Air Base top amid the craggy tors of Dartmoor and on the scenic, windswept summits of the Wicklow Mountains in Ireland. Although these peaks don’t exactly represent an extreme alpine environment, especially during the summer months, they are prone to low precipitation, and the prevailing weather conditions on Dartmoor and in the highlands of Ireland mean it’s always wise to wear a good base layer, and have plenty to put on over the top when the wind starts howling like a banshee, and the clouds come down to meet you.

The Air Base is the foundation garment for Haglöfs’ new L.I.M. ZT II range, and it can be used from sea level to the summit of serious peaks, if paired with the correct clobber from the rest of the range. During my recent adventures, I have been using this base layer alone, and with Haglöfs’ Air Midlayer and GTX waterproof shell jacket.

The ‘cooling’ Polartec Delta fabric used in this top is purpose designed for use during dynamic activity in warmer weather, so hiking on Houndtor and scrambling up the peaks of Great Sugarloaf, Maulin and Lugnaquilla in a temperamental summer – when the weather lurched from heatwave to horizontal rain – was a good test for the Air Base.

And it passed with honors. A bit like Merino wool, the Polartec Delta fabric does indeed possess the power to keep you warm when required – especially when used on conjunction with a midlayer like a fleece top, and a waterproof shell jacket or windbreaker – and cool when you’re working hard in more benign conditions. In my experience, self-generated moisture was effective wicked away from my torso, and the top very quickly dried out even when it became considerably sweaty (especially across the rear, when I was wearing a hiking pack). The Air Base also doesn’t cling to you like an insecure shower curtain when it does get damp, which is nice (and allows the garment to dry out quicker).

It also claims to prevent the build-up of bad odors, presumably thanks to natural enzymes in the lyocell content. I’ve only been wearing the Air Base for a few months so far (and I have taken it off on occasion), so I can’t fully verify this yet, but so far it has remained happily stink free. I love merino, but it is prone to wear and tear, whereas this top feels like it’s hardwearing and tough enough to last multiple seasons – which I would fully expect it to for the high price.

As mentioned, you can wear the Air Base as a stand-alone long-sleeved top, and I have done exactly that on a regular basis over the last few months. It’s not overly tight fitting (even over a gestating Guinness gut), feels good, and provides both thermal insulation from chilly breezes and protective cover from the sun.

While I was never cold while wearing the Air Base, I have been testing it in mainly warm conditions, while engaged in quite vigorous activity (where it excels), and there are certainly thicker and toastier under-tops out there, including some specifically made for thermal performance.

This top is just one piece of the clothing jigsaw in a modular series of layers, however, which Haglöfs’ designers have designed to be combined and used together in the mountains, to offer a level of performance and protection that defies their exceptionally low carry weight. And it does all work beautifully, but there’s no getting away from the fact that it is an extremely expensive ensemble to invest in, if you go for the whole lot. You can, of course, use the Air Base with other more affordable mid- and outer layers.

Also consider