Zeta Primaloft Overbag

Used in combination with your Zeta bag to boost its warmth by 24°C. This specialised Primaloft-filled overbag is also cut to fit over our Ultra K, Minimus and Minim 400 down sleeping bags.
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.
870g / 31oz
Zeta Primaloft Overbag


  • 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: red
  • Options:
    • Deep, insulated overhead cowl-cover in Dri-LX fabric (+250g/+£110) (same colour as selected fabric)
    • Taped outer shell in waterproof Dri-LX fabric (+250g/+£185) (red, white, black, green)
    • No (twin front) zips (-60gr/-£30)
    • Full-length zip (no twin zips) (+30gr/£41)
    • Short or Long lengths
    • Slim or Wide widths

†Please note: We make our stuff sacs big enough to allow fairly easy stuffing rather than reducing the bags to the tightest minimum.

‡Please note: The optional waterproof Dri-LX outer provides an extra seam-sealed outer shell to the bag. While a shelled sleeping bag is not designed to be used alone in heavy rain (the hood area is open to the elements) the shell does protect the bag when it is used outdoors without a tent.


The Zeta Overbag is cut wide enough to go over our Zeta 1 or Zeta 2 Primaloft sleeping bags without reducing their loft. The Zeta Overbag provides a 24°C (41°F) temperature boost to the main bag.

The Zeta Overbag shares the features of the Zeta 1 and Zeta 2  bags.

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, insulated cowl cover (in waterproof Dri-LX fabric) sheds snow. The reflective strip and clip loop confirm this bag is one for climbers in extreme situations.

The optional waterproof Dri-LX outer provides an extra seam-sealed outer shell to the bag.

Used alone the Zeta Overbag has a typical operating temperature of -4°C (23°F) and makes for a roomy bag. 

The Zeta Overbag also fits over our Ultra K, Minimus and Minim 400 down sleeping bags.

Example combinations:


  Combined TOT* (°C)
Zeta 1 + Zeta Overbag -28
Zeta 2 + Zeta Overbag -40
Minim Ultra K + Zeta Overbag -16
Minimus + Zeta Overbag -19
Minim 400 + Zeta Overbag -29


*Typical Operating Temperature (Celsius)

Read our technical briefing on down vs synthetic insulation.


Dri-LX (weight: 64 gsm)

At just 64gsm, Dri-LX is our lightest 2-layer breathable waterproof rip-stop nylon fabric. Its remarkably low weight not only makes for a lighter load, but also reduces pack size. Its excellent waterproofing qualities are in part due to how it can be taped at the seams to create a waterproof shell for sleeping bags and clothing.

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

Works well with
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