UKC

Hi All,

I'm hoping the UKC hive mind might have a contact for the department at Leeds Uni that tests sleeping bags. Such as mentioned in these old UKC articles https://www.ukclimbing.com/articles/features/insulation_explained_part_1_st... https://www.ukhillwalking.com/articles/features/insulation_explained_part_2... Google suggests Mark Taylor might still work there but the Performance Clothing research group doesn't seem to exist any more.

In short, a few of us are interested in settling a "pub debate" on the effectiveness of some of the sleeping bag type insulation we use for mountain rescue. We suspect that others might also be interested as well even if it did start as a pub debate.

Cheers

Andy

In reply to Andy DB:

Maybe get in contact with mountain equipment, don't they have a guy called"Dr down" working for them who I think knows everything about sleeping bags, not just down, so synthetic too

He might be able to easily answer your questions

In reply to Andy DB:

https://ahc.leeds.ac.uk/design/staff/479/dr-mark-taylor

https://www.researchgate.net/profile/Matthew-Morrissey-2

https://www.linkedin.com/in/matthew-fuller-45b01490?originalSubdomain=uk

In reply to Andy DB: contact Mathew Fuller   (ME s Dr Down ) who can probably answer your questions his UKC user name is  Mr Fuller and he wrote the articles you referenced 

In reply to Andy DB:

I can certainly try to answer your question, though with most things about insulation I will preemptively answer 'it depends...'.

In reply to Mr Fuller:

Yes we do suspect the answer might be it depends. The question we actually have is does the ordering of the insulation make a difference. Current teaching is that hypothermic casualties are packages in a casualty bag (fiberpile sleeping bag) and vac mat (full body split) and now usually a blizzard bag as an inner vapour barrier. The question we had was does it matter which order the vac mat and cas bag are used in? When the question was asked people had opinions on why either order would work better hence the want to do an experiment to see if it actually makes any difference 

In reply to Andy DB:

To be clear, you had an argument in a pub focused on if compressing a insulating layer that relies on trapping air to work made it a better or worse insulator?

hold my beer.

<edit for whisky induced spelling issues>

In reply to Andy DB:

To do an experiment on this sort of thing you'd ideally use a thermal manikin which I'm afraid Leeds don't have, and even then it might not represent real conditions very well. But I think it can be mulled over a bit without an experiment.

So to clarify it goes(?)

Scenario 1: casualty/blizzard bag/fibre pile bag/vac mat

Scenario 2: casualty/blizzard bag/vac mat/fibre pile bag

The vac mat is the bit I don't know much about to be honest. Is it essentially a plastic bag filled with foam beads and once the air is expelled it's thickness is negligible? Also, how big is your fibre pile sleeping bag vs the typical casualty: is it oversized? This is probably the most important factor...

In reply to Dr.S at work:

Yes sounds stupid. My working hypothesis is that compressing the insulations should be worse but apparently, others aren't of the same opinion. I don't have any evidence to disprove them, hence an experiment. Is this not how all the best science is done? Their argument is that the vac mat is a large thermal mass that would need to warm up so better not inside the insulation.

In reply to Mr Fuller:

Yes vacmat is a plastic bag with polystyrene beads in covering in fabric for toughness. Wouldn't say it is negligibly thin, is probably 1-2cm thick. When in operation it has the air pumped out so won't have much air to provide insulation. Our case bags are usually a bit over sized (although not for the very large) and also usually have some buckles on the side to tighten them up to remove some of the excesses flap.

There are clearly other considerations that might affect the order but the question was purely which is thermally most efficient

In reply to Andy DB:

To be honest, I’m not sure on the answer to this without seeing all the arranged bits in front of me, and even then without some experiments it would of course still be hypothesis (guessing) only. I have appeared at MREW events in the past so might be able to provide a better answer in the future.

Here’s some general pointers that might be useful in helping you come to the answer. I’m only addressing insulation in this and am not considering practicality in a rescue situation:

- Minimise air flow getting to the casualty or inside the insulation. That might favour putting the air-impermeable vac mat outside the sleeping bag.

- Avoid flapping fabrics. Flapping acts like bellows and will pump hot air out of the assembly. This again might favour putting the air impermeable vac mat outside the sleeping bag.

- Don’t compress your insulation. This applies to both the top of the assembly and the bottom of the assembly. Underneath the casualty you are always going to get compression because of body weight, so sticking something compression resistant but full of air directly underneath them is a good idea. A few mm of closed cell foam is ideal. With the vac mat inside, if the foam ends up really dense and therefore actually quite conductive, that isn’t good. On top of the casualty try not to squash the insulation, but balance that versus flapping fabrics.

- Keep everything as dry as you can. Dry insulation works much more effectively than wet insulation, and warm when wet is a real misnomer. This again might point to the impermeable vac mat being on the outside of the system.

- Avoid systems full of circulating air. If you've a hugely oversized sleeping bag on a small casualty this won't work very effectively and you might be better off taking some of the excess size away by putting the vac mat inside the bag. You can always fill the air space with something else, e.g. other clothing, bubblewrap, etc..

- Consider what ‘feels’ warmest. It’s really easy to forget this, but whatever feels warmest often is, especially if you’re a scared casualty who needs some reassurance.  

- Make sure the Blizzard bag is doing everything it can: don’t compress it too much, try to keep an air gap maintained between it and the casualty wherever possible.

What would happen if the Blizzard bag went round the whole assembly of sleeping bag and vac mat...? From an insulation perspective that’s quite interesting but it’s not necessarily useful for a rescue situation.

If anyone else has any insight I'd be interested to hear it.

In reply to Andy DB:

Is this not just a protest of some kind?