Omicron "K" Down Belay Jacket














Andy Kirkpatrick
Features
- A PHD K Series product: Ultimate warmth / weight ratio
- PHD's Unique 1000 fillpower down
- Water-resistant Ultrashell outer fabric
- Ultralight 10X inner fabric
- Stitch-through construction for lightness
- 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 the back of the hood
- New! Now also available in Custom Sizes. Specify Body Width, Body Length, and Arm Length independently*****
- 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: 13cm x 21cm*
*Please note: We make our stuff sacs big enough to allow fairly easy stuffing rather than reducing the jacket to the tightest minimum.
Description
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...
The Omicron “K” is a down filled superlight belay jacket which squares perfectly with the modern fast-and-light approach to technical water ice and mixed test pieces: a good fit, freedom of movement, minimum weight and maximum warmth are essential, but so is dependable protection on cold stances. The stitch through construction cuts excess weight, while allowing the 1000 fill power down to deliver a TOT* rating of -10°C.
Designed to work over or under a climbing harness, the minimally featured, trim fit makes for light movement while climbing. The fully adjustable helmet hood and high front zip provide maximum warmth, and lock right down in gnarly conditions. Minimalism doesn’t come at the expense of function however: this is a highly technical jacket, and the high-viz reflective strips for location, glove-friendly zip pulls and a clip loop to secure the jacket at change overs are all there because they need to be.
Although down filled Belay jackets are really in their element in cold, dry conditions, the water-resistant Ultrashell fabric and YKK Aquaguard zips help to protect against damp snow or dripping ice if the temperatures rise. If you’re venturing into cold and wet 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.
Please note: If you order a custom-sized version of this jacket it will take longer (approximately 45 days) to be manufactured ready for dispatch. Custom-sized versions of this jacket are not returnable and customer loyalty discount cannot be applied.
Technical
Ultrashell (weight: 40gsm)
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.
Sizing
Standard Sizing
The PHD Sizing Chart below is based on measurements without clothing, exactly the way you would buy a shirt or a sweater. A 42" (107cm) chest means that your bare chest uninflated measures 42". Inside Arm is measured from armpit to wrist-bone.
Size | Height | Chest | Waist | Inside arm |
---|---|---|---|---|
XS | 155-163cm (5'1"–5'4") |
86cm (34") |
71cm (28") |
46cm (18") |
S | 164-170cm (5'5"–5'7") |
91cm (36") |
76cm (30") |
48cm (19") |
M | 171-178cm (5'7"–5'10") |
99cm (39") |
84cm (33") |
51cm (20") |
L | 179-186cm (5'10"–6'1") |
107cm (42") |
91cm (36") |
53cm (21") |
XL | 187-193cm (6'2"–6'4") |
114cm (45") |
99cm (39") |
56cm (22") |
Custom Sizing
Once you've selected a Body Width you can choose Body Length and Arm Length up to two sizes bigger or smaller. For example, a jacket with a medium (M) Body Width can be XS, S, M, L, or XL in Body Length and XS, S, M, L, or XL in Arm Length. If you have any questions about your size, please contact us.
Body Width. Use the chart below to find your Body Width. Measure yourself without clothes, relaxed with an uninflated chest.
Body Width | Chest circumference | Waist circumference |
---|---|---|
XS | 86cm (34") | 71cm (28") |
S | 91cm (36") | 76cm (30") |
M | 99cm (39") | 84cm (33") |
L | 107cm (42") | 91cm (36") |
XL | 114cm (45") | 99cm (39") |
Body Length -- can be two sizes up or down from Body Width. Use the chart below to find your Body Length size. Measure your height without shoes:
Body Length Size |
Your height in cm | Your height in inches |
---|---|---|
XXXS | 139 - 144cm | 4'5" - 4'8" |
XXS | 145 - 154cm | 4'9" - 5' |
XS | 155 - 163cm | 5'1" - 5'4" |
S | 164 - 170cm | 5'5" - 5'7" |
M | 171 - 178cm | 5'7" - 5'10" |
L | 179 - 186cm | 5'10" - 6'1" |
XL | 187 - 193cm | 6'2" - 6'4" |
XXL | 194 - 201cm | 6'4" - 6'7" |
XXXL | 202 - 209cm | 6'8" - 6'10" |
Inside Arm -- can be two sizes up or down from Body Width. Inside Arm is measured from armpit to wrist-bone without clothes. When you measure your inside arm let your arm hang loosely by your side. Don't extend it horizontally.
Inside Arm | cm | Inches |
---|---|---|
XXXS | 41cm | 16" |
XXS | 43cm | 17" |
XS | 46cm | 18" |
S | 48cm | 19" |
M | 51cm | 20" |
L | 53cm | 21" |
XL | 56cm | 22" |
XXL | 58cm | 23" |
XXXL | 61cm | 24" |
N.B. PHD clothing is unisex.
Notes:
- Down Jackets are sized to fit over thermal underwear & fleece.
- Shell Jackets are sized to fit over thermal underwear & fleece or light down clothing (e.g. Minimus Jacket): to cover thick down clothing, go up one size.
- The arms of our outdoor jackets are designed to be long enough to keep your wrists warm when your arms are extended horizontally (when using trekking poles, for example) or when you are reaching above yourself (when climbing, for example). In this respect the arm lengths of our jackets differ from street/fashion jackets.

Reviews
Features
- A PHD K Series product: Ultimate warmth / weight ratio
- PHD's Unique 1000 fillpower down
- Water-resistant Ultrashell outer fabric
- Ultralight 10X inner fabric
- Stitch-through construction for lightness
- 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 the back of the hood
- New! Now also available in Custom Sizes. Specify Body Width, Body Length, and Arm Length independently*****
- 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: 13cm x 21cm*
*Please note: We make our stuff sacs big enough to allow fairly easy stuffing rather than reducing the jacket to the tightest minimum.
Description
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...
The Omicron “K” is a down filled superlight belay jacket which squares perfectly with the modern fast-and-light approach to technical water ice and mixed test pieces: a good fit, freedom of movement, minimum weight and maximum warmth are essential, but so is dependable protection on cold stances. The stitch through construction cuts excess weight, while allowing the 1000 fill power down to deliver a TOT* rating of -10°C.
Designed to work over or under a climbing harness, the minimally featured, trim fit makes for light movement while climbing. The fully adjustable helmet hood and high front zip provide maximum warmth, and lock right down in gnarly conditions. Minimalism doesn’t come at the expense of function however: this is a highly technical jacket, and the high-viz reflective strips for location, glove-friendly zip pulls and a clip loop to secure the jacket at change overs are all there because they need to be.
Although down filled Belay jackets are really in their element in cold, dry conditions, the water-resistant Ultrashell fabric and YKK Aquaguard zips help to protect against damp snow or dripping ice if the temperatures rise. If you’re venturing into cold and wet 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.
Please note: If you order a custom-sized version of this jacket it will take longer (approximately 45 days) to be manufactured ready for dispatch. Custom-sized versions of this jacket are not returnable and customer loyalty discount cannot be applied.
Technical
Ultrashell (weight: 40gsm)
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.
Sizing
Standard Sizing
The PHD Sizing Chart below is based on measurements without clothing, exactly the way you would buy a shirt or a sweater. A 42" (107cm) chest means that your bare chest uninflated measures 42". Inside Arm is measured from armpit to wrist-bone.
Size | Height | Chest | Waist | Inside arm |
---|---|---|---|---|
XS | 155-163cm (5'1"–5'4") |
86cm (34") |
71cm (28") |
46cm (18") |
S | 164-170cm (5'5"–5'7") |
91cm (36") |
76cm (30") |
48cm (19") |
M | 171-178cm (5'7"–5'10") |
99cm (39") |
84cm (33") |
51cm (20") |
L | 179-186cm (5'10"–6'1") |
107cm (42") |
91cm (36") |
53cm (21") |
XL | 187-193cm (6'2"–6'4") |
114cm (45") |
99cm (39") |
56cm (22") |
Custom Sizing
Once you've selected a Body Width you can choose Body Length and Arm Length up to two sizes bigger or smaller. For example, a jacket with a medium (M) Body Width can be XS, S, M, L, or XL in Body Length and XS, S, M, L, or XL in Arm Length. If you have any questions about your size, please contact us.
Body Width. Use the chart below to find your Body Width. Measure yourself without clothes, relaxed with an uninflated chest.
Body Width | Chest circumference | Waist circumference |
---|---|---|
XS | 86cm (34") | 71cm (28") |
S | 91cm (36") | 76cm (30") |
M | 99cm (39") | 84cm (33") |
L | 107cm (42") | 91cm (36") |
XL | 114cm (45") | 99cm (39") |
Body Length -- can be two sizes up or down from Body Width. Use the chart below to find your Body Length size. Measure your height without shoes:
Body Length Size |
Your height in cm | Your height in inches |
---|---|---|
XXXS | 139 - 144cm | 4'5" - 4'8" |
XXS | 145 - 154cm | 4'9" - 5' |
XS | 155 - 163cm | 5'1" - 5'4" |
S | 164 - 170cm | 5'5" - 5'7" |
M | 171 - 178cm | 5'7" - 5'10" |
L | 179 - 186cm | 5'10" - 6'1" |
XL | 187 - 193cm | 6'2" - 6'4" |
XXL | 194 - 201cm | 6'4" - 6'7" |
XXXL | 202 - 209cm | 6'8" - 6'10" |
Inside Arm -- can be two sizes up or down from Body Width. Inside Arm is measured from armpit to wrist-bone without clothes. When you measure your inside arm let your arm hang loosely by your side. Don't extend it horizontally.
Inside Arm | cm | Inches |
---|---|---|
XXXS | 41cm | 16" |
XXS | 43cm | 17" |
XS | 46cm | 18" |
S | 48cm | 19" |
M | 51cm | 20" |
L | 53cm | 21" |
XL | 56cm | 22" |
XXL | 58cm | 23" |
XXXL | 61cm | 24" |
N.B. PHD clothing is unisex.
Notes:
- Down Jackets are sized to fit over thermal underwear & fleece.
- Shell Jackets are sized to fit over thermal underwear & fleece or light down clothing (e.g. Minimus Jacket): to cover thick down clothing, go up one size.
- The arms of our outdoor jackets are designed to be long enough to keep your wrists warm when your arms are extended horizontally (when using trekking poles, for example) or when you are reaching above yourself (when climbing, for example). In this respect the arm lengths of our jackets differ from street/fashion jackets.
