Diamir 900 Down Sleeping Bag: K Series

Warmth to weight taken to the limit with our 'K Series' version of this high-specification expedition bag, cut roomy enough for stashing kit and for comfort at altitude.
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.
-32°C / -25.6°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.
1570g / 55oz
Diamir 900 Down Sleeping Bag: K Series

Performed perfectly on my Spirit of Endurance Expedition [a solo, unsupported and unassisted crossing of the Antarctic]
Louis Rudd MBE



  • 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
  • Inner water-resistant Ultrashell panels
  • Full length zip protected by double draft tubes
  • Pack size: 25 x 44cm†
  • Mummy hood draws up close around head
  • Wide 3D Collar seals in warmth at neck
  • Trapezoid baffle system for ideal down control
  • Special baffle section stabilises down over chest
  • Extra down channels along each side ensure side insulation
  • Side block baffles prevent down shift
  • Ultrashell inner panels at head to protect against breath soaking the down
  • Ultrashell panels at inner foot to cope with damp feet/footwear
  • Footpiece: ovoid shape to fit naturally to feet and avoid pressure
  • Navy blue inner for quick drying
  • Stuff sac with large mesh storage sac
  • Options:
    • Zip location: left or right
    • Short or Long lengths*
    • Waterproof Dri-LX outer fabric shell (+250g)‡

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

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

‡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.


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...

This K Series Diamir down sleeping bag takes specialised mountaineering and expedition bags to a new level of lightness. Built for long and arduous challenges it is cut roomy enough for comfort and for stashing vulnerable kit overnight with you. The trapezoid baffles provide a lightweight method of achieving excellent down control, aided by vertically-oriented chest baffles that prevent any chance of down migration.

  • The Ultrashell outer is highly water-repellent and helps to keep the down dry and lofting.
  • The Ultrashell inner panels in the hood and foot area also protect the down.
  • A large 3D shaped collar, side V channels to insulate the side seams, double draft tube behind the zip, and closely-boxed foot section form part of a formidable list of technical specifications.

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, for example in a snow-hole or under a tarp.

Pictures show Diamir 1200, Diamir 900 is a little slimmer.

Read why Trek & Mountain think this bag is "Fantastically light and warm. Exceptional performance for its weight."

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.

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.

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.


PHD's trapezoid baffle system is used throughout. This is the best of the technical baffle systems, combining excellent down control with low baffle weight. In cross section the baffle system looks like this:

The design has a close-fitting down-filled mummy hood, and side V-channels which ensure all areas of the body are insulated. The baffles over the chest are vertically aligned, which stops any horizontal shifting of the down caused by arm movement during the night.

More on sleeping bag construction.

Proofed inner panels

Proofed fabric (Drishell or Ultrashell) panels are included inside the hood and foot areas of the bag to help keep the down dry. In very cold temperatures your breath can cause ice to form around the face opening, which may soak into the down as it melts. The panels at the foot end are to protect the down if you get into your bag with wet socks (or in extreme situations with your boots on).

"Performed perfectly. Really liked its light weight. The bag always lofted really well and I was never cold once. It was the perfect solution for this particular journey."
Louis Rudd MBE, using the Diamir 900K on his Spirit of Endurance Expedition, a solo unsupported and unassisted crossing of the Antarctic land mass.

"Fantastically light and warm. Exceptional performance for its weight. The hood ... was one of the best in the test, and it felt one of the warmest bags too; this perhaps was due in some part to the double baffles along the main zip and the tapered shape, as well as the quality and quantity of the down in the bag."
Chris Kempster, Trek and Mountain Magazine's test of Expedition Sleeping Bags.

"I spent over 90 nights in the PHD Diamir 900, and not a single one involved a shiver while sleeping. I slept in my unheated van at trailheads in the San Juans before ice climbing and ski trips; in tents in the mid-winter desert; under a blanket of stars on multi-day ski tours; and everywhere in between.

The Diamir 900's 900 fill down had an unbelievably high weight-to-warmth ratio, as one would expect. Couple that with an almost perfect fit and a waterproof outer, and this bag proved to be perfect for this past winter and for future cold weather expeditions.

I highly recommend this bag to anyone looking for a lightweight, compressible, very warm winter bag that looks like it will last for many seasons to come."
Sam Feuerborn.

"Thank-you for the superb sleeping bag."
Robert De Mey

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