A few years ago I was trying to figure out how to drop weight from my overnight kit. I started by weighing all my items and it was obvious that the sleeping bag was the first area I needed to look at.

Big Brands Don’t Cut It

At the time I had been using a North Face Inferno -29C bag, which came in at just below 1800g. For a mainstream product it’s fairly light and small but I knew there must be a better option for me. I knew after looking at the big brands that I would have to go custom or to one of the smaller specialized brands, in order to drop serious weight but after looking I still felt like the product I was looking for wasn’t out there. I started drawing designs to create a DIY “deep winter” half bag.

Half Bags?!

Half bags have been around for a while but for some reason they haven’t seemed to reach a wider market. The design is simple, you put the bottom 2/3rds of your body in a bag and wear your down jacket to bed. Since the design can be very simple (no zippers, hood, etc) and you are taking a down jacket for camp anyway, you save a lot of weight in the end.

Sleeping in near the summit of Gordon on the Wapta Icefield. Photo by Chris Moneypenny.

Custom Made

While doing research on sleeping bag design I kept coming across a company I had not heard of before. DIY’rs seemed to think they had the “ultra light” design thing figured out and after looking on their site I seemed to agree. I decided to email PHD about my design idea, even though their site said they didn’t take unsolicited emails about new product designs! To my surprise they replied saying they liked my idea and would see what their team thought. Less than a month later I got news that they had created the Xero Half Bag with my basic concept in mind. I ordered two (no, I didn’t get one for free, which I was 100% ok with) and after the first use I knew I would never go back to a full length bag.

The Xero

The Xero Half Bag is basically what you would get if you cut the top 1/3rd off of a mummy bag. The fabric and down quality are better than what you will find in most mainstream products and the result is a sleeping bag that preforms in cold temps and weighs only 725g.

Enjoying a hot meal in bed.

Xero Face Fabric

The Xero Half Bag uses the very light Ultrashell coated fabric for it’s outer shell and a 15 denier mini-ripstop nylon called Superlight MX fabric for the inner. Even though this fabric is thin and light, it still holds up in a winter environment just fine as the Ultrashell is water-resistant. I have slept in many crammed snow caves where I regularly found myself rubbing against snow without seeing any performance issues. One cold night my partner woke up to realize she had fallen off her sleeping mat and had been sleeping directly on the snow but had no problems with the bag’s performance.

High End Down

When I tell people that PHD uses 900-1000 down I often get push back, “there is now such thing as 1000 down”. Admittedly I had my doubts before getting PHD product in my hands but after altering my Xero Socks I realized that there is a massive difference in the down quality coming from PHD. The Xero Half Bag uses 950 down and it’s crazy how much room it fills for so little weight. I’m not going to get into what “950 down” means and there are a lot of myths or misconceptions about down numbers. PHD has written an awesome primer about all this on their website and explains it better than I would have in this review so check it out!

Fabric Extender

Since this design was for extreme winter environments an upper fabric extender was included in order to protect from wind and snow. I have found this add-on to work great for the design’s purpose and also to store extra down items inside if need be. The original design had the waist drawstring on the outside of the bag and I had told PHD that if it were inside it would be easier to use. I do not know if they changed this for future/current product.

Bag Design

The Xero Half Bag uses a box wall construction to allow for full loft (measured at 7.5cm on my bags). It has side block baffles to prevent down shift and an extra down-filled side V channel along each side of the bag. In the end it means there are no weak points in the design to allow for cold air to sneak in. Regardless if you sleep on your back, side or front you will have maximum even loft.


The design is meant me to simple and effective, which means there aren’t many “bells and whistles”, (which is good thing when trying to go light!). The only extra included was a reflective strip of material added to the outside of the foot box, this makes it very easy to find at night and adds no weight. A welcomed addon for those hazy midnight washroom breaks.

But Is It Warm?

One of the biggest misconceptions out there is that products provide “warmth”, while they actually only insulate. Your body is the heater and the down/product is the insulation. With that said I have found the Xero Half Bag to work just as good as my previous sleeping bags when matched with the correct jacket. It is very important you have a jacket that matches the temps you will be sleeping in! I have done some testing to this point and in extreme temps I was cold when I didn’t use a jacket that matched those temps (we are talking very cold here, -40C while using a poorly matched jacket made for -10C). Generally I always have a large basecamp jacket when camping, my go to currently is a PHD Rondoy Down Jacket K Series. I also carry one or two lighter down jackets on most trips which I can layer (or put inside my fabric extender) for when temps drop. Layered sleep systems like this are key to warmth, flexibility and keeping everything light, again PHD has written about this on their site.

A compressed Xero Half Bag

Too Specialized?

I know what you might be thinking, “I don’t need this because I only camp once and a while and I don’t want another sleeping bag”. There’s no reason you can’t use the Xero Half Bag as your only winter bag. Although I rarely stay in huts, I have used the Xero Half Bag for such trips and found it to work great as you can just layer down if the hut is too warm. The bonus is having a bag that can handle colder temps in case something happens before getting to the warm hut and you are forced to bivy for the night. In the end to Xero is just as light or lighter than many lower end “hut” bags too. I see it as “flexible” and not “specialized” on this point.

Is The Xero Half Bag For You?

I’m not going to lie, half bags aren’t for everyone but I’m 100% converted! The light weight and small pack footprint can not be beat and if you already bring a large basecamp jacket (my experience in the mountains says you should) then you probably won’t notice a difference in the bag style in regards to warmth. In the end sleeping systems are one of the most difficult things to get perfect and that is because all of our bodies are different. I’m not going to tell you the Xero Half Bag will work for you absolutely. Anyone that says “this one sleeping bag works for everyone” is either being paid to say that or lacks experience to comment, because it’s bullshit.


It probably seems like I’m pushing PHD a lot in this review and it’s because they make sweet products and write truthful gear articles. I’m not sponsored by them nor have I ever got a kick back from sales of their products. I had to buy my Xero Half Bag just like everyone else and the pictures you will find of me on their site were provided free to them. I support them in these ways regardless of sponsorship or deals because of who they are and their purpose, to find out more about PHD click here. To view the Xero Half Bag click here.

6 thoughts on “PHD Xero Half Bag”

  1. Have you seen the Patagonia one? It has a uninsulated top ‘vest’ to keep the half bag up and drafts out. Seems like a great design.

    However my question has always been on the basic premise of Half bags:
    -That you are somehow saving weight-
    Let’s say you need 7.5cm of down loft to stay warm at night:
    A system with this half bag would have you using this, combined with a parka 7.5cm thick.
    If it is cold enough to be wearing a 7.5cm thick parka, I would definitely want something on my legs too in camp!
    The only exception I can think of would be multi day climbing routes, were you are on a (porta)ledge at night, so can’t move around, so you can use the half bag even when awake.

    Instead, a sleeping bag filled with 2.5cm loft on the body, and 5 cm on the legs, would combine with a 5cm parka and 2.5cm pants.

    More realistically, for winter camping, you need, let’s say 15cm of loft.
    A 10cm thick half bag, combined 5 cm thick down pants, would need to be paired with a 15 cm thick parka! Extremely unwieldy (box baffles that thick around the arms?).

    Besides unwieldy giant parka’s the other thing I don’t understand is weight/warmth ratio: it is lighter to add warmth to a sleeping bag (over the upper body in one go) than to a parka, where it needs to go around the torso and arms individually.

    I totally see the half bag for mild weather, where a moderate parka is all you need to keep warm at night.

    1. I also own the Patagonia half bag but only use it in spring/summer/fall or on hut trips in the winter.

      I am saving a ton of weight with my half bag. I don’t change the clothing I take on overnight camping trips and this bag is over 2lb lighter than my previous one. My normal camping kit includes down pants and a very big basecamp jacket for hanging out, which I then just go to bed in.

      15cm of loft for a sleeping bag is crazy thick. My Xero has about 8cm and I have slept down to -40C in it now – paired with my big basecamp jacket and down pants. Everyone is different and I sleep warm but a 15cm loft bag is something you’d take in the very high mountains or arctic I’d say.

      1. Thank you for your reply.
        I was probably off on my down thickness, will measure better later. And of course as you said, different people have different warmth needs.
        Anyway, I was just picking a number. My main question was about the system of a half bag and “super”parka vs full length bag and “regular” parka, for a given amount of insulation.

        I (and I assume most people) also wear a warm parka for winter camping, and I wear it to bed too. I guess the difference comes from the fact that my parka is most definitely NOT warm enough to keep my upper body warm while sleeping in cold weather!
        But, that of course is personal choice.

        I still was curious about the half bag+pants+‘Superparka’ being lighter than an equivalent warmth thinner parka+ pants+ full length sleeping bag.

        I looked at PHD to compare these systems.
        .Starting with the Xero half bag. They list that as -30C, so we will use that as an example.
        Xero half bag, plus Xero jacket*= 1975g

        Rondoy jacket and pants, rated -10C sleep use*, weigh 1020g.
        Greenland400 bag weighs 795., total system weight 1915g.
        According to PHD’s overbag page, a -5 bag like that, adds about 23 degrees, so also around -30C for the total system.

        Surprisingly close!

        *Clothing temp rating is for “low to moderate activity”, so I subtracted 10 degrees for comparison with sleeping bag ratings, which are for zero activity.

        1. I guess it depends on what you compare…in your example you are bulking up on clothing for half bag use, when in my experience I wouldn’t do. I would debate you are comparing apples to orange in your example.

          My setup is:
          Xero Half Bag – 725g
          Rondoy Jacket K Series Jacket – 500g
          Wafer Down Trousers K Series Summer Edition – 110g
          Total – 1335g

          The Greenlandic 400 is a -5C bag, what I think you’re saying in your example is that you would add the over bag to it in order to get down to -30C, but then in your stats above you don’t add the extra 940g, so it’s not even close.

          If you wanted a better comparison I would look at something like the Hispar 800K bag, which is 1100g, then add your basecamp clothes. Still, the Xero half bag is almost 300g lighter so I don’t understand how you think a half bag would be the same? Again, regardless if I have a half bag or a full bag I would be using the same base camp clothing setup.

          1. Aha, that last sentence is the key.
            I was going on the assumption that, if I have a full sleeping bag covering my torso, then I don’t need to bring as warm a parka.
            So yes, I agree if you choose to bring a Parka warm enough to keep your torso warm at night, while sleeping, then there is no sense in a full length bag.

          2. I mean… I literally said the same thing in the review and my other replies…

Leave a Reply

Your email address will not be published. Required fields are marked *