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.
200g / 7oz
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
  • Sheer-light 7X fabric
  • 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
  • Elasticated side panels for closer fit
  • Drop-tail back
  • Cuffs: light Lycra
  • Hem: elasticated
  • Stuff sac*
  • Pack size 13 x 21cm
  • Options:
    • Stud on superlight down-filled hood
    • Fabric: Water-resistant Hypershell (Red or Blk,  + 15g, +£16)

*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 7X inner fabric, the exceptional lightweight components used in this jacket, have allowed us to make a sub-zero down jacket at 200gm (7oz) 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 windproof 7X fabric.

It shares the pared-down design principles of the whole Ultra range: light Lycra cuffs, waist-level front pockets, zipped inner security pocket, and a drop-tail back. Together with elasticated side-panels, for a closer, warmer fit, great performance is guaranteed.

The outer fabric can be upgraded to water-resistant Hypershell to elevate the performance at just a very small increase in weight.



Ultralight 7X fabric (weight: 22 gsm)

7X is our new sheer-light 7 denier fabric. An exquisitely fine rip-stop nylon, 7X is incredibly light, highly wind-resistant and has first-rate down proofing. This fabric helps us create the very lightest of gear in the PHD range. Of course the lighter the fabric the lighter the sleeping bag or down clothing, and the less space it takes up in your rucksack. This fabric is so light it actually helps to allow even greater lofting of the down too.

Water-resistant HyperShell fabric (weight: 28 gsm)

HyperShell is PHD’s exceptionally lightweight waterproof coated fabric. This remarkable ripstop nylon provides complete windblock and good water resistance at a breath-taking weight (28 gsm). HyperShell protects the down from condensation drips found typically in tents, tarps and snow-holes, but its very low weight allows greater lofting of the down and a smaller pack size. Hydrostatic head: 1000mm.

Note: unlike some other so-called 'proofed' fabrics, HyperShell does not rely solely on a DWR (durable water repellent) coating. Although it has a DWR coating, more importantly it has a breathable and permanent PU coating applied on the underside of the fabric that cannot be abraded through daily use, so performance is maintained over many 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.

Works well with
From 203.32 90g
Unbelievably light down-filled sock for warm feet in cold tents. 
From 835.48 585g -5℃
Warmth to weight at the limit of possibilities with this 'K Series' version of...