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Leaving a SIM on a bedchair with sleeping bag (21 posts / 3,408 views)
Churchy Churchy
Posts: 1,333
Post #16 23 Jan 2026 15:53
2
In reply to Post #2
Exactly the same for me, been using a SIM for years and never even considered doing it differently. Once you start folding the bed up with the valve open you can hear the air releasing pretty quickly. Then sit on bed folded so you can strap it closed nice and tight, its then under a fair bit of pressure with the SIM folded in two places so its not likely to reinflate. This method also means you are opening and closing the valve the least amount of times, which can only be good for the life of the valve.
Baza1075
Posts: 552
Post #17 25 Jan 2026 21:41
1
As wandle says a thermarest and a tiny pump. Pump air in and out. Very comfy and deflates to nothing.
roman
Posts: 4,847
Post #18 26 Jan 2026 15:22
1
Haze outdoors YouTube cut open his old SIM after many years of self inflating by mouth. And there was no moisture mold nothing
SamB
Posts: 93
Post #19 26 Jan 2026 17:01
0
In reply to Post #18
My understanding is that the "don't blow air in" idea is for inflatable pads with down insulation - as down does not perform as well if its soggy. I didnt think it applied to SIMs with cellular foam structures.

As to whether the soggy down theory is really a thing or a myth - I don't know. I'm not even sure how much more moist breath is compared to the ambient air - I guess that depends on if you had to set up your brolly before your bedchair ot not...

wandle1 wandle1
Posts: 7,469
Post #20 26 Jan 2026 19:21
0
There is a big difference tween a self inflating mat ( sim) and a straight pump up ,blow in /up manual mat with a duo lock valve ..

Other things can affect a mat or SIM such as R value and type of conditions that its used upon

For example ,doing a thru hike in cold conditions ,and not using insulation underneath can cause a lot of condensation when mouth inflated ,as the mat would be a compact roll up job and not necessarily a SIM ,remember this is for true minimalism and not comfort ..in that scenario it's why those little pumps are used ,especially if your tired or expel straight into a standard non SIM ,a pump will also deflate the mat , even a SIM faster which makes it easier to leave on a bedchair after deflation with the valve closed and not open ..leaving a valve open on a bedchair ,using a SIM ,means the SIM is fighting to inflate ,its under pressure in a folded and creamed up bedchair ...I'd most likely not do that ,but I would with a thermarest type of mat ,of which there are many variations..


( I've done winter camping ,using mouth inflation it does get mould in inside the mat)

A genuine SiM ,only takes a couple of puffs to make them viable to use ,however every model I've had ,including some well known makes have deflated during sessions ,and it's why I prefer a Thermarest ..as this type is more compact and long lasting ,but more expensive..

There's a lot more to the above than people realise, and it's a continuous learning curve ,
Chuffy Chuffy
Posts: 6,794
Post #21 28 Jan 2026 12:08
3
In reply to Post #1
I've had a Helium on either a Solar SP or Wychwood Compact for years. Just open the bed and leave it for 15 minutes, do the valve up. When putting it away undo the valve and fold the bed up, it's that simple.
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