Ultra Down Jacket: K Series

Our lightest sub-zero down jacket. A 'K Series' product. Warmth to weight at the limit of possibilities for extra-keen lightweight backpackers and mountain racers. 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.
-5°C / 23°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.
240g / 8oz
Ultra Down Jacket K Series

The sensation of immediate warmth is unsurpassed. The 1000-fill is so high-lofting, it puffs up as if a pump has been attached. Rare and wonderful.
Judy Armstrong in TGO Magazine. Read full review.



  • A PHD K Series product: Ultimate warmth / weight performance
  • PHD's Unique 1000 fillpower down
  • Water-resistant Ultrashell outer fabric. An excellent balance of weight, water-resistance and breathability
  • Superlight 10X inner fabric. Down-proof, wind proof and super soft
  • Stitch-through construction for lightness
  • Full length lightweight front zip
  • Insulated under-baffle with wrap-over chin guard
  • 2 hand-warmer pockets at waist level
  • Internal, zipped security pocket
  • Drop-tail back
  • Cuffs: light Lycra
  • Hem: elasticated
  • Stuff sac*
  • Pack size 13 x 21cm
  • Set Options:
    • Stud on superlight down-filled hood

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


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...

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, choose your body width, and then the body/arm lengths, shorter or longer, 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.

1000 down and 10X inner, the exceptional lightweight components of the K Series, have allowed us to make a down jacket at 240gm (8oz) which weighs less than most down vests. But make no mistake, this Ultra Jacket is a piece of real outdoor kit: the 1000 down gives surprising warmth inside the highly water-resistant and windproof Ultrashell outer.

It shares the pared-down design principles of the whole Ultra range: elastic at side-waist, light Lycra cuffs, waist-level front pockets, zipped inner security pocket, and a drop-tail back.


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.

"The sensation of immediate warmth is unsurpassed. The 1000-fill is so high-lofting, it puffs up as if a pump has been attached; this is enhanced by wide baffles, which allow the down to expand so quickly. Weight is kept to a minimum through simple but effective design. Overall it was a dream to wear. PHD is the only company in the world using 1000-fillpower down in clothing and sleeping bags for expeditions and mountaineering: rare, indeed, and wonderful."
Judy Armstrong in TGO Magazine. Read full review.

"Your kit is AMAZING !! Wow - very impressed. I'm a really cold person but even on my own in a tent at -8°C I was comfortably warm. It's also incredibly light. So light, the organisers made me take extra items to MAKE UP weight in my bag!"
Rebecca Ferry, using the Jacket in the Everest Trail Race, where she came in 4th in the women's race.

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