Overall View
A lot to spend on a baselayer but soon pays its way with fewer washes needed while saving weight and pack bulk. Easy clean on the trail. Some find merino itchy and some feel outsourced production doesn't meet New Zealand's original quality but judged on its own merits the Icebreaker Mondo Zip is sublimely comfortable and highly effective in both its wicking abilities and its odour resistance.

Real World Test
Baselayers are perhaps the most undervalued and most often overlooked items of the typical outdoors wardrobe, often little more than an afterthought when the budget's near enough gone. Without a well selected baselayer, however, the whole layering system falls at the first hurdle, and on examination a large proportion of outer shell shop returns come down to a poor base layer selection. Icebreaker's Mondo Zip is designed to complement mid and outer layers by actively wicking chill-prone perspiration away from the body to the outside from where it can progress to the outer layers and be evaporated away.

I'm obsessed with base layers.  They are the foundation of the layering system, in fact you could say they are the base from which all other active clothing perform. A £500 jacket is useless if the base layer doesn't allow it to transmit moisture and a thermal mid layer is redundant if the item under it doesn't wick and or conducts heat away from the body.

To be honest Rab's not a company that's best known for its base layers, having made a name and reputation based around its down and insulated products, so when the MeCo 165 LS Zip landed for test and review we weren't expecting anything special. Even more so at the idea of yet another merino/something else hybrid. OK we got it wrong!
Getting the name out of the way first the MeCo part refers to Merino and Cocona (a fibre derived from coconut shell) while the 165 is a reference to the weight - there's also a 120 option. The LS is Long Sleeve and the Zip refers to the YKK zip that gives ventilation. The Cocona is treated with "active carbon" which helps speed up evaporation of water through increasing the yarn's surface area. Combined as 35% Cocona and 65% Merino the idea is to have all the odour resistant and comfort properties of merino while adding the wicking and drying advantages of synthetic fabrics.
Testing over a continuous five day period the MeCo proved to be one of the best uses of merino in a hybrid fabric, retaining the majority of the advantages of merino while making a noticeabl;e difference on both the amount of moisture it can handle and the speed at which excess is evaporated. It's close to the feel of merino, if a little "thinner" feeling and while 5 days doesn't compare with the 30+ days we've worn a Chocolate Fish Merino for previously there was no noticeable issue with odour resistance.

One of my favourite outdoor clothing items of all time is my Rab down jacket. The quality, warmth and fit have been very hard to beat and I have worn the jacket a great deal. I would buy another. So, testing a Rab baselayer wasn’t going to be a hardship! I am a big fan of Merino wool. It’s the best fabric for keeping you warm and dry (quick drying when sweaty) and also has a handy knack of not getting too pongy. 1005 polyester baselayers do a good job as baselayers, too, but they usually stink of body odour after only a few hours of wearing while active.

The Rab women’s MeCo 165 long sleeve baselayer

Sizes: 8 - 16

Weight: 200g / 7 oz

Colours: Rose, amethyst, black

Fabric: 65% Merino/ 35% recycled polyester

Price: RRP £65 (have seen for less)

Contact: Rab