Back to top

Please select a color/size.


  • Silkweight Phasic SL panels at back of knees reduce bulk while improving thermal regulation
  • Anatomical shaping with flatlock construction reduces bulk while improving thermal regulation and moisture transfer
  • Gusseted crotch and stretch fabric give you unrestricted mobility
  • Comfort waistband with laminated, soft-brushed finish; non-chafing label


View all Arc'teryx Men's Long Underwear Bottoms

REI membership


Best Use Multisport
Fabric Polyester
Moisture Wicking Yes
Quick Drying Yes
Underwear Weight Midweight
Inseam (in.) Unavailable
Gender Men's

Size chart

Sizing notes

SHORT: Some pants are available in short sizes, which generally means an inseam that is 2 inches shorter than regular sizes. TALL: Some pants are available in tall sizes, which generally means an inseam that is 3 inches longer than regular sizes.

Rated 5 out of 5 by from Phasic magic for your bottom half. I own several of the Phasic tops, and cannot praise them highly enough. These bottoms fully live up to expectations. Just like the shirts, they are supremely comfortable, have a great, tight fit for enhanced wicking, and move sweat away incredibly fast. Great as an extra warm layer on very cold days, and I also use them in conjunction with waterproof overtrousers alone on warm, humid, very wet days. Removing the additional layer on warm days help keep you cool and dry. Material is surpringly durable. Length is perfect for me. Just above the ankle, so they don't interfere too much with a hiking sock. Yet another great product.
Date published: 2013-04-12
Rated 4 out of 5 by from Fantastic materials and design, just wish they were slightly longer I love the stretch, feel and durability of these bottoms — superior attributes in comparison to other manufactures' merino long johns which I also own. The material's intrinsic stretchiness allows a great next-to-skin fit and also makes taking them on/off simple. As with the AR tops, the bottoms' smoothness and material weight is very comfortable and lets you slip other layers over them easily. The combination of the smoothness and stretch also makes them feel very durable and far less susceptible to pilling. The Phasic SL patches behind the knees aren't a gimmick and work well. Unfortunately their fit prevents them from being perfect for me. I'm 6'2", slim and wear medium (as with the AR tops which fit perfectly). I find the bottoms to be about 3/4" short in the leg and the rise — I have other base layer bottoms (also in medium) which are more generous in both areas. For me the rise is the bigger issue because this makes them feel less secure (and this might apply beyond taller wearers). They aren't hipsters but a more 'natural rise' would be my preference for an active-use base layer. These will be really fantastic bottoms if your body is a shorter-medium.
Date published: 2013-01-08
Rated 5 out of 5 by from Love it! Comfiest base layer I've ever had in my gear list. Very comfortable pant, wicks away sweat like nothing, and doesn't cause any itchiness on the skin, barely even feel them there. Perfect for all around or yearly resort skiing, never finding them too warm or too cold, just right. Really nice pant to wear jogging in the winter as well. Cheers! Enjoy em!
Date published: 2012-12-05
Rated 5 out of 5 by from Perfect These do exactly what's needed. Nobody get excited by buying base layer leggings, they are not a new set of axes! If you need some buy these they work perfectly!
Date published: 2015-12-13
  • y_2017, m_6, d_21, h_24
  • bvseo_bulk, prod_bvrr, vn_bulk_1.0.0-hotfix-1
  • cp_1, bvpage1
  • co_hasreviews, tv_0, tr_4
  • loc_en_US, sid_110620, prod, sort_[SortEntry(order=RELEVANCE, direction=DESCENDING)]
  • clientName_rei-inc
  • bvseo_sdk, java_sdk, bvseo-4.0.0
  • CLOUD, getReviews, 122ms
  • bvseo_sdk, java_sdk, bvseo-4.0.0
  • CLOUD, getContent, 86ms
  • bvseo-msg: The resource to the URL or file is currently unavailable.;