Zeta 1 Primaloft Sleeping Bag

Specialised Primaloft-filled bag for climbers' bivouacs in damp conditions. Reliable comfort on an overnight belay ledge.
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.
-4°C / 24.8°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.
777g / 27oz
Zeta 1 Primaloft Sleeping Bag with twin front zips

Last week I climbed the North Face of the Eiger ... Both my self and my client used your Zeta sleeping bags. They were just fantastic and completely idiot proof.
Mark Seaton.



  • Outer Fabric: water-resistant Ultrashell
  • Inner fabric: super-light MX
  • Synthetic Primaloft Gold insulation, edge-stitched for maximum loft
  • Twin 2-way zips at front for access and for armholes for cooking etc.
  • Large inside chest pocket
  • Stuff sac with clip loop
  • Pack size: 23 x 40cm
  • Reflector strips for night location
  • Clip-loop for securing
  • Hood draws up close around head
  • Footpiece: ovoid shape fits naturally to feet
  • Colour: Blue
  • Options:
    • Deep overhead cowl-cover in red HS2 fabric (+75g/+£83)
    • Taped outer shell in waterproof HS2 fabric (+200g/+£165) (red)
    • No (twin front) zips (-60gr/-£30)
    • Full-length zip (no twin zips) (+30gr/£41)
    • Short or Long lengths
    • Slim or Wide widths


Recently redesigned

Updated with Primaloft Gold filling and a greater range of build options, the redesigned Zeta 1 synthetic sleeping bag is now 35% lighter and more compressible than before. The new, taped water-proof HS2 shell and overhead cowl options boost the bag’s performance in extreme conditions.

Combine with the new Zeta Overbag to extend the use of this specialist bag from -4°C to -28°C.


Designed specifically for climbers' bivouacs in damp conditions, with all the advantages of Primaloft-Gold synthetic fill and water-resistant Ultrashell outer fabric. The twin front zips, an extra bivvy feature, double as arm holes for cooking and gear sorting. The large inside chest pocket keeps stashed kit warm. An optional cowl cover (in red HS2 fabric) sheds snow. The reflective strip and clip loop confirm this bag is one for climbers in extreme situations.

Read our technical briefing on down vs synthetic insulation.

Ultrashell (weight: 40 gsm)

One of the lightest of PHD's coated materials. This ripstop nylon provides complete wind block and good water resistance at minimal weight. Ultrashell gives an excellent upgrade to performance with very little weight penalty.

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 PHD's high-spec 2-layer ripstop for waterproof outers on our down. It is light enough to be the optional taped shell on our sleeping bags and tough enough for expedition use in our Omega clothing. HS2 is completely waterproof (when the seams are taped) and offers excellent breathability.

Note: these comments relate to an older version of the warmer version of this bag

"Last week I climbed the North Face of the Eiger ... only the 2nd time a British Guide has done this. We had two bivys on the face and one on the summit. Conditions were difficult and we wore crampons for the entire route. Both my self and my client used your Zeta 2 sleeping bags. They were just fantastic and completely idiot proof. "
Mark Seaton.

Works well with
From £129.00 145g
Primaloft-filled mountaineering mitts. Confidence and warmth in cold and wet conditions.
From £436.00 870g -4℃
Used in combination with your Zeta bag to boost its warmth by 24°C. This...