(Copied from a FB post by David Stibbards)
So last event people got cold at night, and though we don’t expect the same conditions next event this is one of the few areas I am qualified to comment and might be helpful, plus this has been going around in my brain for a while.
Dadford is a cold site and it always will be in April, where the average perceived temperature for mid-April night times is pretty much ZERO. There are a few reasons for this.
- It’s between the Downs and the Cotswolds, which runs SW/NE meaning no wind break from the prevailing wind OR from a cold Northeasterly. Guess which we had that chilly Thursday and Friday night…
- It’s a local valley. The IC camping area is where the cold air from the surrounding area pools – In Dawn and Wintermark especially (which is why it is both Glorious and Heroic to camp there).
- The OC camping is better but even more exposed to the wind – best place to camp is IMHO in the woods with the Navarr/Orc where the warm air gets trapped, but obviously winter means fewer leaves and it’s a mostly deciduous copse IIRC.
- IC tents are COLD. I know, I know, canvas is a better insulator than thin nylon, but that only matters if you are putting out enough warmth to make an appreciable difference in a 15-25 cubic meter bell tent. Which you aren’t unless you are Johnny Storm or your camping troupe is a flesh pit (in both cases slide into my DMs, especially you, Johnny). An OC tent with 3-4 cubic metres of volume will warm up and retain some of that heat.
So tent aside, warmth comes from 3 things;
Sleeping bag
We all know about layering. Great. You need this. But not everyone knows about the ORDER of layers. I heard several people say ‘I put a blanket over my sleeping bag but was still cold’ for example. Do not do this. Your sleeping bag (or any ‘lofted’ quilt or cover) gains its warmth by having big spaces between the fibres/feathers inside to trap warm air. Placing anything on top of this will compress these fibres and quickly lead to diminishing returns. If you are inside a tent your sleeping bag is best as the outermost layer.
So what should be inside your sleeping bag? Now we are working with a confined space which gives us some helpful constraints – we need to start as close to your skin as possible; if you haven’t joined the pyjama party you are sleeping on (ha ha) the best thing you can do – a dense, close-to skin layer like thermal underwear. Why are tights/leggings warm? Because they trap warm air close to your legs and this exactly the same. Between pyjamas and the sleeping bag we don’t have a lot of space, so light, thin layers are the only real option. The other reason for this is compression again. If your sleeping bag is too small you have probably noticed your knees, hips and elbows getting cold – this is because they press up against the filler of the sleeping bag and basically reduce it to a thin screen. Thick layers will do this for you too – instead go for one or at most two sleeping bag liners – thin, soft people-pockets you wriggle into and form that extra air-catching layer.
As for choice of sleeping bag, there is a risk of getting technical here because the ‘2/3/4 season’ classification is not great and I don’t want to suggest people get a special warm sleeping bag just for cold events. That said, from a major retailer I don’t think there is ever a time/place in the UK I would recommend a 2-season. They just make too many compromises to actually succeed in keeping you warm at the 5 degrees they claim. Go for a 3 season as your default. Make sure it fits, your feet should not quite be at the end and it should be snug but not tight to your body. A hood is ideal, if not you will want to adapt something into one that doubles as a neck baffle.
Consider your body’s natural tendencies, a lot of people may find they are ‘hot’ or ‘cold’ sleepers - women particularly will want to take any temperature ratings with a grain of salt as they are strongly gendered and that’s not clear on the labels. Literally, the specification is based on the ‘standard male’ and ‘standard female’. I like to think this couple are Brad and Janet. Most people are probably more Riff-Raff/Magenta.
Wash your sleeping bag you filthy animal. Over time the synthetic fibres (and especially down) lose their loft and/or acquire grease from your body. Wash like its wool and tumble dry if you can with either tennis balls or wool dryer balls. Do this before E1 and you’ll be fine until the end of the year. Unless you are expecting company in which case (1) I suspect you’ll be plenty warm and (2) double sleeping bags are a thing but there is no dignity in hot-pocket hanky-panky. Note that a sleeping bag liner will avoid the need for frequent washes, and extend the life of the bag. There really isn’t a good reason not to pick one up if you can.
Sleeping mat
At this point if you are still cold, it’s either your sleeping bag is just not right for you or what you are sleeping on. Remember compression? A lot of hikers actually use quilts rather than sleeping bags because the bag beneath you is completely compressed – it’s basically worthless. If you have a thick, heavy blanket this is where it should be. But what is beneath that? Most people have a sleeping mat, and this is the only place where I’ll get even slightly technical – there is actually a formal, industry a rating system (R-value) for sleeping mats from 1 upward, 5 is alpine, 1 is a glorified lilo. For good night time warmth in April in the UK 2.5+ a good place to be. That’s not a big ask you’ll find they cost the same as lower ratings as the only real difference at the 1-3 level is thickness. Inflatable pad or solid, this R-value is used for both even at major retailers. A last note on Mylar/reflective blankets – these work ONLY on radiated heat, not conducted. Don’t bother putting these under you.
This does not cover camp beds, and very little has been done to study these (no R-values), but as a general rule of thumb if you use a fishing bed you probably scoff at shivering Citizens but a thin fabric camp bed is probably not ideal – my working theory is though you are off the ground you have maximum circulation beneath you, so while not in contact with the ground directly (the worst of all things) cold air will continue to circulate beneath you, whipping away any leaking warmth from your chilly butt. Hang your blanket over the edges if you have one to prevent this circulation. I expect a similar principle applies to large air mattresses – too MUCH air to warm effectively. There are lots of reasons to use this sort of thing but a big thick layer of wool under you (which doesn’t compress like a lofted bag) is the best way to go.
Your insides and you
You can prepare for bed better. Most importantly, think about what you have been eating or drinking. A hot meal will keep you warm into the night, many of us go to bed quite late. If you aim to sleep at time-out but ate dinner at 6/7pm you won’t be getting any benefit from the 2-3 hour boost to your temperature. Have a hot drink before bed and/or eat closer to 9/10pm.
Timing is important for when you go to bed too. Your body cools as you sleep, and is more tolerant of the cold. Get to bed earlier (yeah, right) and your body will cool off as the temperature drops, allowing for a more comfortable night.
Alcohol. Alcohol makes you feel warmer because it opens up your capillaries and flushes your skin. This makes your core colder as the air will greedily whisk away that heat. Once the former wears off you are stuck with the latter – alcohol is very much bad for you if you are cold. (That fictional image of the St Bernard with brandy around its neck is actually a fluffy murder-machine and the only benefit you’d get if you had hypothermia is a goodbye nightcap).
Fin
So that’s the highlights of a lazy Saturday morning for me with maps, topographic and temperature data and rectal body temperature studies. I hope this helps at least one person adapt for April next year!