Icebreaker Women’s Merino 200 Oasis Long Sleeve Crewe: Tested

By Liz Ginis 27 June 2023
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Icebreaker touts the Oasis Long Sleeve Crewe as “the world’s best base layer”. We put that claim to the test climbing Tassie’s highest peak in late autumn.

“World’s best base layer”. That’s one helluva claim from the team at NZ-based Icebreaker. And never one to shy away from a challenge, AusGeo Adventure decided to put the Icebreaker Women’s Merino 200 Oasis Long Sleeve Crewe Thermal Top through its paces… on a climb up Tassie’s highest peak, Mt Ossa (1617m), on a near-freezing day in late autumn.

But our gear test began days earlier at the start of Tassie’s Overland Track. A pre-dawn start, and a brisk 4-degree temp, called for multi layering and yep, you guessed it, the first was my merino wool – berry-coloured – long-sleeved crew neck. With a fabric weight of 200gsm (the higher the fabric-weight number the warmer you’ll be, with weights ranging from 125–400), it was, I hoped, warm enough to ward off the morning chill and light enough that when the sun heated things up later in the day I wouldn’t steam. 

I needn’t have worried. The day didn’t warm, in fact it clung belligerently to single digits as we trekked along duckboard, around pandanus, and up the steep, rocky route to Marion’s Lookout and the clouded-out summit of Cradle Mountain. And then the rain came – nay, almost sleet – and by the time we reached our hut beneath towering (and completely obscured) Barn Bluff, I worried whether the 200 was nary a wise choice at all.


There’s a lot to like about the design of what is a fairly basic-looking long-sleeved top, one that can be worn as an around-the-house staple when the air has a bit of a nip to it, and every day when you’re on the trails. I’d tested mine out up and down coastal headlands while training for the Overland – the 100 per cent merino wool masterfully regulated my body temp – but the proof would be in the main event, hauling a heavy pack up, down and around mountains over six days of hiking.

I’d also carried a weighted daypack to get my shoulders and legs primed, and the base layer’s gusseted underarms made swinging it on and off easy – they allow for extra movement and comfort – while the offset, flatlock shoulder seams did a great job of preventing pack rub. I’m also partial to a drop-tail hem, which the top has, for added coverage when you take a breather and plonk yourself down on the forest floor. (No bum crack or tramp stamp exposed here!)

In the field

Day 4 on the OT started early. With more than 7km of walking ahead of me as well as the side trip to the peak of Ossa (roughly 5 hours there and back), I was up with the extremely early birds. Decked out in the base layer, then a fleece and finally a lightweight down jacket (and, obviously, the obligatory hiking pants, gaiters and boots), I dashed off. I’d tackled Heartbreak Hill the day before but, for mine, this morning’s climb from the hut to Pelion Gap (1113m) – the jumping off point for Ossa – was far more taxing on the body’s blood pumper, and the down jacket was peeled off and stowed around halfway up. By the time I reached the weathered timber sign pointing out the duckboard track heavenward, I was down to my base layer.

Testing the Oasis Long Sleeve Crewe for Aus Geo ADVENTURE was tough. Please believe us… Shaun Mittwollen

True to its ‘bodyfit’ claim, it hugged my upper body and torso perfectly and that fabric weight of 200 was the perfect one for the blue-sky day. I dumped my tortoise shell, loaded up my day pack (fleece and rain jacket, just in case the weather turned, and scroggin) and set off, climbing up Mt Doris, on the way to the steep skirt of Mt Ossa, before scrambling over enormous boulders, below skyrocketing dolerite pipes and beside precarious drops. It was sweaty work, especially up a few of the vertical climbs, but through it all the base layer kept me comfortably toasty. On reaching the summit, the wind picked up and I wondered about sweat chill. I needn’t have bothered. The merino had wicked away most of the moisture, leaving me dry and, despite my exertions, relatively unstinky.

The final word on the Icebreaker Women’s Merino 200 Oasis Long Sleeve Crewe

At around 180g-ish, this base layer is an ideal lightweight addition to your gear set for multi-day hiking (I took three with me on the Overland), and it’s versatile enough for regular duty across other outdoor activities. It is my go-to for trail running at the moment, and if the night’s particularly cold, it does double duty as a PJ top. There are five colourways (black, griftstone heather aka grey, midnight navy, grape, go berry and purple gaze aka mauve) and there’s also a scoop-neck version (black and mink).

After more than two months of testing, in a variety of conditions, the Icebreaker Women’s Merino 200 Oasis Long Sleeve Crewe is still going strong.

So, is this indeed the world’s best base layer? I’m not one to deal in absolutes, but as we shiver through what meteorologists are labelling “another dramatic week of winter weather” with “extreme cold” forecast for most of the country, it’s definitely on high rotation.

RRP: $110. For more info see Icebreaker.