Kappa Trousers

Our warmest synthetic-insulated mountaineering trousers. Waterproof fabric and Primaloft Gold-fill to cope with really rough and wet conditions. Now also available in custom sizes.
Typical Operating Temperature
Guideline minimum temperature. Sleeping Bag TOT: you should get a night’s sleep, under normal circumstances. Clothing TOT: you should feel warm enough, assuming low/moderate activity. Sleep System TOT: relates to full system. For more details, see our Technical Briefing.
-10°C / 14°F
For clothing, weight is for size: M. For sleeping bags, weight changes with selected length/width. N.B. there may be some variation in the weights of finished products.
475g / 17oz
Kappa Primaloft Insulated Trousers


  • Primaloft Gold® synthetic insulation (100gr/m weight).
  • Outer Fabric: Waterproof HS2 (un-taped for lightness).
  • Inner Fabric: Superlight MX.
  • Edge-stitched for maximum loft.
  • Short side zips with over baffle.
  • Crampon patches.
  • Articulated knees.
  • Fly zip with baffle.
  • Elasticated waist with cord adjustment.
  • Stuff sack.
  • Pack size: 13 x 21cm.*


* Please note: we make our stuff sacs big enough to allow fairly easy stuffing rather than reducing clothing to the tightest minimum.


Also available in custom sizes. We make clothing to order, so if you’re not a standard size we can make it to fit. To order a non-standard custom size, select the Custom Sizing tab and choose the waist and inside leg sizes that work for you. A custom size takes us a little longer (typically two weeks longer) to make and, because it’s personalized, it’s non-returnable and our customer loyalty scheme can’t be applied.

These Primaloft filled trousers are designed as a versatile lightweight answer to lower body warmth for Himalayan trekking, Scottish winter excursions or Alpine winter sport. Pair them up with the Kappa Jacket for a complete system.

Excellent protection is provided by the HS2 waterproof outer* and quick body warmth by Primaloft Gold® , which will retain much of its insulation when it's wet. These trousers also work well when you're already soaked and simply want a warm-up layer to shift the chill.

Short side zips and high abrasion crampon patches provide practical use at minimum weight.

*Please note: although the outer fabric is waterproof, the stitch lines are un-taped for lightness. So, although the outer will shed rain and snow, in a heavy downpour water can penetrate the stitching. However, the Primaloft® insulation retains much of its insulation if wet. As always in the mountains, if there is a possibility of prolonged rain, carry full specification waterproofs.

Superlight MX fabric (weight: 32 gsm)

A mini-ripstop nylon with excellent tear strength, MX is the pick of the superfine 15 denier downproof materials. We have tested lighter fabrics, but most have had significant drawbacks, while our confidence in MX is based on several years of extensive use in both our ultralight and our high mountain gear.

Primaloft Gold®

Primaloft Gold® is the ideal microfibre insulation. Ultrafine fibres produce an insulating core that is incredibly soft, lightweight and water resistant. In our experience it absorbs water much more slowly than other waddings, a marked advantage in wet-cold conditions.

The nearest of the synthetics to the feel of down, yet tougher than you would expect. Primaloft Gold® offers the best warmth/weight performance in the Primaloft range

Waterproof HS2 outer fabric (weight: 88 gsm)

HS2 is a 2-layer laminate, a high-spec option for the outer layer of our insulated gear. This ripstop fabric strikes an excellent balance between lightness and durability. It is light enough for our Belay tops and tough enough for expedition use in our Omega clothing, while the Kappa clothing makes full use of both its qualities. HS2 is completely waterproof (when the seams are taped) and offers excellent breathability. (Weight: 88gsm).