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Best Lightweight (~200g) Thermal Sleepwear Bottoms

Rab's Power Stretch Pro Pants impressed in the cold and wet

Rab's Power Stretch Pro Pants


As always, we're looking at the Rab Power Stretch Pro Pants from the point of view of long distance trekking over tough terrain.

Test subject: Waist 33", Inner Leg 30", Height: 5ft 8"
Test item: Size = Large
Kit Tests: Winter, Summer (multiple)
Disclaimer: None required (item not provided by manufacturer)


Materials: Polartec Power Stretch Pro (Polyester / Polyamide (Nylon) / Elastane) 53% / 38% / 9%
Weight (Size Large) 201g
Product Sizing Reference: 33" Waist, 30" Inner Leg = Large
Manufacturer RRP £65.00

Manufacturer's Page


Scramble Review

Introduction: What do we want?

When covering long distances over multiple days and weeks, you really need two types of clothing: one for trekking, the other to change into when you're done for the day. Here, we're looking at the latter, what we classify as sleepwear but is really also camp/tent wear.

What we're after is a good warmth to weight ratio (since you're carrying these items much of the time), durability - specifically the ability to maintain shape (since form is function and this kind of item gets quite a bit of push and pull) and in turn maintain its thermal and wicking properties - and perhaps as importantly, comfort, since morale should not be underestimated.

Overkill, but only at first glance

Outdoor clothing is often very expensive and the Rab Power Stretch Pro Pants could be regarded as overkill for our recommended use, as they're primarily a winter climbing base or mid layer. But after many years, we've come to the conclusion that with thermal sleep / camp wear, if you get the right item, you only need one set for all seasons (see below). The beauty of Rab's Power Stretch Pro Pants is that they're light yet very warm (even when wet), very durable, designed specifically to hold their shape over time, breathable, fast wicking and to top it off, are cosy and comfortable. So they tick all the boxes ... but they're not cheap.

Rab's quick drying Power Stretch Pro PantsThe Power Stretch Pro Pants drying out fast. Patch sold separately.

We'll look at some of the additional factors that have brought us to the Rab Power Stretch Pro Pants. But first, what is Power Stretch Pro?

Power Stretch Pro (PSP) is a fabric designed by Polartec. It has a durable nylon face with a polyester fleece interior and elastane mixed in to provide the stretch.

Elastic Fantastic

One of the issues we've had with many thermals we've tested is that they're often great to start with, but over time their elastic properties diminish, they lose their shape and with it some of their thermal and baselayer properties. This has not been the case with Rab's (and others) PSP garments; nor should it be since Polartec designed PSP precisely to address this issue:

Stretch fabrics need dependable strength properties to consistently recover their original form after being pushed and pulled during activity. If an elastic fabric structure is overstretched it becomes permanently damaged and loses the ability to regain its original shape and performance qualities. This is why Polartec® Power Stretch® Pro™ is engineered with greater tensile resilience as a key feature of its construction. The next-to-skin surface keeps you warm and dry through touch points that diffuse and evaporate vapor moisture in the outer layer. Reinforced elastic fibers ensure the fabric consistently rebounds after every stretch. Polartec® Power Stretch® Pro™ wicks moisture and regulates breathability like a base material with the fortified ability to handle direct exposure to the elements.

That's the key to the PSP Pants. They operate like a very warm baselayer, but can handle the elements. So they work well as an outer layer when camped up in the mountains and can handle a broad range of nighttime temperatures.

The Power Stretch Pro's waistband, flatlocked seams and fleece innerMoisture wicking waistband, flat-locked seams and fleece lining


There aren't a great many features to discuss. The PSP Pants have a comfortable "moisture wicking waistband" (see above), and flatlock seams throughout. The key to their warmth though, is the brushed fleece lining:

A closer look at the fleece innerPolartec's warm fleece lining works well in the wet

Thermals aren't just for Winter

In milder temperatures, wearing warmer sleepwear reduces the onus on ones sleeping bag to keep you warm, meaning you can carry a lighter bag. There's probably a scientific scale (or there should be) to show this, but in our experience, in warmer weather additional grams in the sleepwear department are more effective than additional grams in the sleeping bag. Conversely, as the temperature decreases this becomes less and less the case. Someone really needs to study this.

When sleeping outside, it's far easier dealing with being too hot than too cold; sleeping bags are easy to vent and it's rare during Summer nights that winter thermals alone are sufficient to keep you warm enough for a good nights sleep (assuming your tent / bivvy is not a boil in the bag suffocation unit).

So assuming one goes out in cold as well as warm weather and wishes to avoid shelling out for multiple sleepwear configurations, it makes sense to wear effective winter thermals in summer as this reduces the weight required for a summer bag. In our 2016 summer test I wore what many would deem over the top thermals (the bottoms under review here with Odlo's Warm Originals Sports Underwear Top), however this meant the sleeping bag of choice weighed only 450g and there were some relatively cold summer nights.

A useful backup in case temperatures plummet

In Scramble's 2017 Winter Kit Test the major issue was not so much the cold, but the wet. It rained, hailed or snowed (mainly rained) almost constantly over the 7 days. So although the temperature only hovered around zero in the evenings and early mornings, it felt very cold. No matter how skillful you may be, when the air and the ground are saturated, and everything around you is soaking wet, eventually you are too, and so is all your kit. In such conditions, clothing that is warm when wet is essential. Rab's PSP Pants had performed really well in the much colder Winter 2016 test, but it was how they performed in the wet that really impressed me.

Turned out nice againIn the wettest part of a wet country at a wet time of year (North Wales 2017).

For Winter trekking purposes, it would have to be seriously cold (at least -15 C and below) for me to consider wearing these when active. But it's helpful to have a backup, where if you do get wet and suddenly the temperature plummets, the PSP Pant are there for emergencies.

A Cautionary Tale

You may have noticed in the pic above, a small patch on the left leg - that's not a Rab feature. If your feet are wet, don't try to put on the PSP Pants while standing (especially when you're exhausted and liable to lose it a lot).

The PSP Pants' fleece inner seems to like wet feet and doesn't want to let them go. I went for a particularly stupid brute force approach and ripped them where my feet had jammed, causing a tear about 3 or 4cm across the seam. This is not at all an indictment against the robustness of the PSP Pants (any fabric would have ripped under that force), but since then, if my feet are wet (or damp, or moist), I now put the PSPs on sitting down.

Not indestructible, but easily repairable

We like stuff that's easy to repair

What I learned from that though, was that it's very easy to make lasting repairs with Polartec's Power Stretch Pro fabric. To be ultra-safe and to make the repair hold, PSP (not related) Spinnaker Repair Tape (a sticky nylon ripstop tape which is really ideal for tents fabrics, sleeping bags and insulated jackets, but also works fine with Polartec PSP) protects the stitching on the outer face and makes a durable and lasting repair.

The wonders of PSP Spinnaker Repair Tape

Any Negatives?

The only negative for us is the price. But if these are on offer, grab a pair and you won't need another for a good long while.


Conclusion & Rating

Rab's Power Stretch Pro pants will keep you warm in and around your tent whether you're pitched in soaking bog or on arid rock, whether in freezing cold winters or on cool summer nights. They're extremely warm for their weight and are warm when wet, they're durable (and if you're daft enough to rip them, after you've been warned, they're easy to fix); they maintain their shape after years of use; they're breathable, yet offer a fair degree of wind resistance; they dry out in quick time and transport moisture very effectively, and to cap it off, they make a very comfortable pair of mountain pyjamas. So, although they were designed for a more active role, we think Rab have made the ideal post-trek thermals, which is why their Power Stretch Pro Pants are Scramble's top pick in the Lightweight Thermal Sleepwear category.


Product Images


Rating (out of 10)

RRP Value *

* The value score is derived from two factors:
1) Competitive Market Price (CMP). This represents our judgement of a competitive online price point if we were to stock the item. e.g. if we feel we would need to sell an item at 40% off (i.e. 60% of its full RRP) to be competitive, then our CMP score will be 6/10.
2) Customer Value Price (CVP). We then make an honest appraisal of the maximum price we would be willing to pay for the item (and we're mean). So if we'd pay 80% of its RRP our CVP score would be 8/10.
We then average the two scores to get our final value score, which in our example would be 7/10.


Last Updated: 30/04/17

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