Winter in the central Australian desert is cold, very cold! Try minus 5 degrees C on occasion, you could be sleeping above the snowline at that temperature. To stay warm in a compact hiking sleeping bag under those conditions requires a seriously warm sleeping bag.
If you are buying a sleeping bag for your swag, or car camping, that’s a different situation; you can purchase a monster sleeping bag plus additional quilt for that application. This post is about selecting a compact sleeping bag suitable for hiking.
Minus 5, really? Yes, here’s the reality; lets say you are going out in the West Macdonnell Ranges for a hike, the forecast for the nearest centre, Alice Springs, is 2 degrees – not uncommon in the winter months. But, that temperature is measured in a Stevenson Screen at 1m above the ground on the plains adjacent to the airport, you will be sleeping on the ground, commonly in the lowest part of the landscape among the ranges where the coldest air ‘ponds’ & stratifies at night, so take 2-4 degrees off of that forecast minimum and add to that the fact the forecast minimum can actually get down into the minuses; you can see why it feels so seriously cold in the early hours of the morning out there – because it is!
You may think, well the water in my water bottle didn’t freeze so it can’t have been below zero, but think about how long it takes to freeze a liter of water in the freezer at home, it takes quite a few hours, so the chances are it may have gotten below freezing but not for long enough to freeze your water. By the way, sometimes the water in your water bottle does freeze!
So how do you choose the right sleeping bag? That’s made easier these days because most sleeping bag manufacturers worth their salt send their sleeping bags off to Europe to be subjected to the ISO EN 23537 (formerly EN13537) rating assessment. A thermal manikin is placed in the sleeping bag which produces four temperature results; upper limit, comfort, lower limit, and extreme.
These ratings are taken assuming that the subject is using a sleeping pad, tent and is wearing a base layer of thermal underwear. For the purpose of the test two thermal manikins are used representing a “standard man” (assumed to be 25 years old, with a height of 1.73 m and a weight of 73 kg), a “standard woman” (assumed to be 25 years old, with a height of 1.60 m and a weight of 60 kg).
This brings us to the point that everyone sleeps differently; men generally, but not always, sleep warmer than women, and physically large people generally sleep warmer too. Most people have a fair idea from experience as to where they fit on the warm sleeper scale.
To cut a long story short the two important figures you need to scrutinise are comfort, and lower limit.
If you are an average woman or slightly cold sleeper the comfort rating is the minimum temperature at which you will be sleeping comfortably. Once the temperature starts to fall below the comfort rating you will start to feel a little chilly and won’t be sleeping comfortably. As the temperature falls a couple of more degrees to the ‘limit of comfort’ rating you will be awake and wishing morning would come and end the suffering – not a great way to prepare for a big day of bushwalking!
If you are a warm sleeper your comfort temperature will extend down the range by up to 5 degrees, so you will be comfortably sleeping somewhere near the limit of comfort temperature and starting to feel the cold as it drops below that.
So that’s it! Firstly make an honest assessment of how cold or warm you sleep and then look at the ‘comfort’, and ‘lower limit’ ISO EN 23537 rating on the sleeping bag & make your decision. Easy!
Ok, so there might be a little more to consider, like price, weight and size but you’ve made the first and most important step. Now you just need to weigh up the options available to you that you feel will meet your warmth requirements based on the ISO EN 23537 rating.
Tip; for winter hiking in the Central Desert and ranges, you’ll probably want to go for a down filled bag to keep the size and weight under control. You may find that a synthetic filled bag, while being cheaper is a little too bulky, then again for the dollars saved you may decide you can live with a synthetic bag. Main thing is you’ve made your choice based on being warm enough and that’s the most important thing.
Oh yeah, don’t forget about those thermals, the mat, and the tent required to ensure the sleeping bag performs at those temperatures as stated!