Hispar Down Overbag: K Series

Warmth to weight taken to the limit. 'K Series' version of a bag used to boost the warmth of your existing sleeping bag by 24°C. Can be used as a stand-alone too.
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.
-6°C / 21.2°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.
710g / 25oz
Hispar Overbag K Series, shown with Hispar 500 sleeping bag inside (Hispar 500 must be purchased separately)

Thank you for the fantastic equipment. I was sound asleep in the Hispar Overbag when my tent-mate spent all night awake and shivering whilst in an (allegedly) -18C bag fully clothed!
Graham B, on a trip to Aconcagua.



  • Overbag to boost warmth. Or an ultralight summer bag by itself
  • Cut wide enough to accommodate a Hispar 400, 500 or 600
  • PHD 'K Series': Ultimate warmth/weight performance
  • Unique PHD 1000 fillpower Down
  • Outer: Ultrashell water-resistant fabric. An excellent balance of weight, water-resistance and breathability
  • Inner: Superlight 10X fabric. Down-proof, wind proof and super soft
  • Box-wall construction for max loft
  • Short zip protected by double draft tubes
  • Pack size: 17 x 28 cm†
  • Straight-wall baffles for lightness
  • Side block baffles to prevent down shift
  • Extra down channels along each side ensure side insulation
  • Oval footpiece to fit naturally to feet and avoid pressure
  • Mummy hood draws up close around head
  • Collar seals in warmth at neck
  • Stuff sac with mesh storage bag
  • Options:
    • Waterproof HS2 outer fabric shell‡
    • Slim, Wide and Extra Wide widths*
    • Short, Long, and Extra Long lengths*
    • Full zip (left or right)

†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 HS2 outer is a complete extra outer shell, with seams taped for weatherproofness. The extra layer of fabric adds considerably to the weight and bulk of the basic bag. It increases the weatherproof qualities of the bag in mountain or Arctic situations, but it is not a substitute for a proper bivvy bag when sleeping out in the rain.

*Please note: For all length or width options, we change the amount of downfill to keep the warmth (TOT) the same.


This K Series product has been created for one single reason, to take warmth-for-weight performance to the limit of what's possible. Unique 1000 down, super-light materials, and specific design features mean that the word Ultralight now applies to this wide range of gear that will take you to the Poles as well as on a Sahara Marathon. More on the K Series...

Your Hispar 500 was fine on Kilimanjaro. If you add the Hispar Overbag, the double bag will take you up Everest. And you still have two different bags to use separately in warmer places. The versatility of the Overbag needs no further comment.

Of course combining bags is also about economics. When you are moving up the expedition scale, you need better gear at each level, and it can be frustrating not to be able use the perfectly good sleeping bag you already have.

One option is to go ahead and buy exactly the item you need for the next level: this will provide you with the lightest, most efficient bag for the expedition, as long as you can afford it.

The cheaper option is to look at the Hispar Overbag. It is cut to fit over the Hispar 400, 500 or 600 and will add about 24C of insulation to the inner bag (see examples below). It will also accommodate a 500 or 700 bag from our Baltoro or Diamir ranges.

Just one last point about this bag. The extra width means that there's room to wear down clothing inside. So as a stand-alone bag it not only offers warmth at –6°C , but you can take it to much lower temperatures with different kinds of down gear inside, even a down suit.

Bag TOT* (C) Bag combination TOT* (C)
Hispar Overbag -6    
Hispar 400 -9 400 + Overbag -33
Hispar 500 -15 500 + Overbag -39
Hispar 600 -21 600 + Overbag -45

*Typical Operating Temperature (Celsius)

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.

Ultralight 10X fabric (weight: 26 gsm)

10X, PHD's first 10 Denier Fabric. 9,000 metres of the yarn used to weave 10X weighs just 10g, that's about the same as a £1 coin! For all its thinness 10X is amazingly downproof and with reasonable care will go on giving you good service for years.

Sleeping bag zips

  • No zip: The standard design on our lightest bags with open hoods. The simplest/lightest system which is a must for adventure racers. Up to 140gm (5oz) lighter than a full zip with draft tube.
  • Full zips: Full zip bags ventilate well, so they can be used over a wider range of temperatures.
  • Short zips: Short zips are lighter and pack smaller than full zips. A short zip & draft tube is up to 85gm (3oz) lighter than the full version.
  • Our full briefing on sleeping bag zips.

1000 fillpower down

This rarest of all downs we reserve for the K Series. European goose down of unique quality. 1000 provides the highest warmth-for-weight performance possible from down. More on our down insulation.


This bag has an insulating straight wall baffle system throughout (no straight-through stitching). Straight wall is the lightest of all baffle systems. In cross section it looks like this:

Side V channels, and double draft tubes behind the zip optimise insulation.

More on sleeping bag construction.

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.

Reviews relate to standard Hispar Overbag, which is 190g heavier

"Thank you for the fantastic equipment. I was sound asleep in the Hispar Overbag when my tent-mate spent all night awake and shivering whilst in an (allegedly) -18C bag fully clothed!"
Graham B, on a trip to Aconcagua.

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