M.Degree Overbag 'K'

Our lightest-ever Overbag, boosting your sleeping bag's warmth by 20°C. A 0°C sleeping bag in its own right.
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.
0°C / 32°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.
480g / 17oz
M.Degree Down Overbag (in red) Black bag not included.


  • Our lightest-ever Overbag
  • A perfect fit and warmth boost for our M.Degree° Bags, and also our Ultra, Minimus and Minim 400 bags
  • PHD's Unique 1000 fillpower down for lightness and warmth
  • Water-resistant Hypershell outer (our lightest-ever proofed fabric)
  • Sheer-light 7X inner fabric
  • Box-wall construction throughout for maximum loft
  • Hood draws up close around head
  • Footpiece: Ovoid shape to fit feet & avoid pressure; multibox section covers whole foot area
  • Straight-wall baffles for lightness
  • Stuff-sac & mesh storage bag supplied
  • Packed size: 13cm x 21cm*
  • Colour: Red
  • Options:
    • Long or Short zips, Left or right
    • Waterproof Dri-LX outer fabric shell (+220g)‡
    • Slim, Wide and Extra Wide widths†
    • Short, Long, and Extra Long lengths†


* 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: 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.

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


Get all-year-round versatility by using an Overbag with your light inner bag. Only carry the lightest sleep system you need.  In summer just pack your lightest bag, in autumn and spring pack just the warmest, and then in winter take both bags.

Overbags (which go over your standard sleeping bag) have been a firm favourite of our clients from the start. They were the start-point for our Sleep Systems framework, and kicked off a new approach to layering up of down gear to sleep in. Now the latest developments in lightweight fabrics have made us look again at the full potential of using an overbag.

Our M.Degree° sleeping bags are amongst the lightest down bags in the world, and we wanted to design an exceptionally light Overbag to pair with them. Cut wide enough to go over our M.Degree° Bags, the pairings make some of the lightest and most versatile Sleep Systems ever made. Boosting the performance of your inner bag by a huge additional 20°C, the M.Degree° Overbag is also a wide stand-alone 0°C bag in its own right.

  Typical Operating Temperatures
Inner bag Inner bag Inner bag + M.Degree Overbag M.Degree Overbag
M.Degree° 100 +10°C -10°C 0°C
M.Degree° 200 +4°C -16°C 0°C​
M.Degree° 300 -3°C -23°C 0°C​
M.Degree° 400 -9°C -29°C 0°C

For summer and winter races, trekking all year round, or for mountain climbing in the Alps, Andes and Himalayas, the M.Degree° Overbag really opens up the possibilities.

The M.Degree° Overbag also fits perfectly over our Ultra, Minimus and Minim 400 bags and our Design Your Own Superlight & Lightweight bags (up-to 400 downfill) .

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.

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.

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.

Sleeping bag zips

  • No zip: The standard design on our lightest bags with open hoods. The simplest/lightest system which is a must for adventure racers. Up to 140gm (5oz) lighter than a full zip with draft tube.
  • Full zips: Full zip bags ventilate well, so they can be used over a wider range of temperatures.
  • Short zips: Short zips are lighter and pack smaller than full zips. A short zip & draft tube is up to 85gm (3oz) lighter than the full version.
  • Our full briefing on sleeping bag zips.

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.


This bag has an insulating straight wall baffle system throughout (no straight-through stitching). Straight wall is the lightest of all baffle sytems. In cross section it looks like this:

More on sleeping bag construction.

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