Delta "K" Down Belay Jacket

A box-wall, down-filled jacket for exceptional warmth on bitterly cold, dry belays. Designed especially for challenging days on classic mixed mountain routes and technical steep water-ice. 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.
-20°C / -4°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.
485g / 17oz
Delta "K" Down Belay Jacket

"PHD ... make fantastic hooded down jackets that provide huge levels of protection (the PHD Delta for example)."
Andy Kirkpatrick.



  • A PHD K Series product: Ultimate warmth / weight ratio
  • PHD's Unique 1000 fillpower down
  • Water-resistant Ultrashell outer fabric
  • Ultralight 10X inner fabric
  • Box-wall construction for warmth
  • Front closure - 2 way YKK Aquaguard water-resistant zip with bottom locking stud
  • 3 insulated pockets:
    • 2 zipped waist level pockets
    • 1 zipped chest pocket
  • Integral hood with wired peak, sized for a modern climber's helmet:
    • Adjustable front cord with ends tethered inside the hood
    • Wired peak
    • Volume reducer on back of hood
  • Reflector tape on front and back for night location
  • Clip loop to secure jacket at change-overs
  • Double exit adjustable hem cord
  • Cuffs: adjustable Velcro tab, to go over or under gloves
  • Drop-tail back
  • Stuff sac
  • Packed size: 17cm x 28cm*

*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.

As steep water ice and mixed test pieces get increasingly technical, so must the kit for the climbers who tackle them: that’s why we designed the Delta “K” Jacket.

However the routes may develop, protection from the cold on frozen stances is still a must, but for modern fast-and-light ascents, so is a good fit, the freedom to move, and minimal weight for maximum warmth.

This exceptionally warm belay jacket houses our unique 1000 fillpower down in box-wall construction, allowing maximum loft and delivering a TOT* rating of -20°C: very reassuring while belaying on frozen waterfalls.

Minimal features and a trim fit mean the Delta can be used in classic belay mode – over the harness when you stop moving – or under the harness for light, easy movement while climbing in deep cold. A fully adjustable, helmet-compatible hood is a given on a serious belay jacket; we’ve teamed it with a high front zip to provide maximum warmth and lock out gnarly conditions. Although clean and uncluttered, there’s no compromise on technical function: features such as high-viz reflective strips for location, glove friendly zip pulls and a clip loop to secure the jacket at change-overs make for a high-spec mountain workhorse.

Down filled Belay jackets really come into their own in dry cold, but obviously the conditions can change: water-resistant protection comes in the shape of Ultrashell fabric and YKK Aquaguard zips, to guard against damp snow or dripping ice if the temperatures rise. If you know you’re heading for wetter conditions though, take a look at our Primaloft filled Belay Jackets.

Please note: this jacket is designed and sized to be worn over the top of outer layers. It provides additional warmth on cold belays and can be swapped between climbers at pitch change-overs. If you want a trimmer, more athletic fit select the next size down.

*TOT: Typical Operating Temperature

Outdoor photography: Paul Horsman.

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.

Reviews relate to previous Delta Belay Jacket, not this brand-new version

"PHD ... make fantastic hooded down jackets that provide huge levels of protection (the PHD Delta for example)."
Andy Kirkpatrick.

"The Delta Belay jacket you made for me has a totally bulletproof feel about it that puts my old Patagonia DAS Parka to shame. The hood is superb and the sizing is perfect to go on over my normal winter climbing gear."
Chris W.

"I've been using your Delta belay jacket for a couple of years and really like it."
Jeff Ingman.

"This is a lovely piece. It's badass protection."
Petesy (a.k.a. Peter Macfarlane).

Works well with
From 1,347.29 885g -21℃
Warmth to weight taken to the limit with our 'K Series' version of this...
From 191.64 150g
Primaloft-filled mountaineering mitts. Confidence and warmth in cold and wet conditions.