Foam mat insulation for inflatable mat in Snow

[crollsurf]

I have a Thermarest Neo Xlite with an R value of 3.2 which I use most of the time.
I just bought an Onda II closed cell foam mat with an R value of 1.5-2. I bought it for mild-hot season hiking and as extra thermal protection when sleeping on Snow.
I would like of shorten the foam mat to about thigh length but not sure what affect it will have regarding heat lose when on snow with my Xlite on top.

Does anyone have any experience in this area? Will any part of my inflatable mat touching the ground mean I lose all insulation from the foam mat, or is it more of a relative thing. If the foam mat protects 80%, then I should still get 80% of the insulation, or my body will be fine but my feet will get cold...

FYI I currently use a 1mm foam mat that has a reflective lining with my Xlite on snow. I wouldn't say I wake up cold but I definately don't wake up warm either.
Maybe I need an Xtherm but hard to find that money when I'll only use it 2-3 nights some years.

[crollsurf]

Just after I posted I solved my problem. Cut the foam mat to size and keep the off-cut for the snow. Punch a few holes so I can tie it together when I need too.

Still interested in how all that works though

[Lamont]

I got an Onda a couple of months ago but haven't chopped it yet. The plan was to put the 1200mm bit inside the Rsack in 3 folded layers against the back panel and the leftover (width cut to about 45cms from the 54) in the mesh front pocket as a sit pad. Combine the two pieces at night, in mild weather, ridges to ridges, under the shoulder to hip region, for a super light mat. Cold weather- maybe as a safeguard. But the shelter then won't fit in the top of my Rsack! Seemed like a good idea at the time. Still working out the best way to use it. Sounds like you have a good idea. On the snow I suppose you put the flat side of the Onda against your Xlite, in case the ridges allow cold air in and under the Xlite?

[andrewa]

Are you asking whether having a longer inflatable mat over a shorter foam mat will result in any trapped warm air in the inflatable escape where there is no underlying foam mat?

I can’t see how it could happen. Heat loss is vertical. If you have foam under a bit, that bit will be warmer.

As an aside, I often wonder why people buy long sleeping mats if they are side sleepers. You only need to insulate your torso pelvis, and thighs. Below this can sit on spare clothing, rucksack etc.

A

[Neo]

I use a similar combo to Lamont, but can't vouch for the 'science' or snow use.

I cut a Nike foam mat bought from Big W to 1400mm long and take it as an extra to an air mat. Put it under the tent floor or tarping groundsheet as protection for the floor and for the air mat when I pivot and where my torso lies.

The offcut bit of foamie works as a sit pad, foot pad or any combination, or for day outings use but usually it stays home.

[Orion]

It would be an issue with an old-style inflatable mattress, the kind without any sort of baffling so that convection currents move the warm air all around. But not with an Xlite.

For what it's worth my wife has used just her Xlite in the snow without issues. I know it's not supposed to be warm enough but it was for her. A thin foam mat is a good idea though. If no other reason it will at least give you something to insulate from the snow when your Xlite pops in the middle of the night on a winter trip.

[Orion]

Is this really a techno question or just a gear question?

[crollsurf]

Are you asking whether having a longer inflatable mat over a shorter foam mat will result in any trapped warm air in the inflatable escape where there is no underlying foam mat?

I can’t see how it could happen. Heat loss is vertical. If you have foam under a bit, that bit will be warmer.

As an aside, I often wonder why people buy long sleeping mats if they are side sleepers. You only need to insulate your torso pelvis, and thighs. Below this can sit on spare clothing, rucksack etc.

A

That's interesting, so a shorter underlying mat will work just as well in the area's that it covers.
I use my pack, spare clothing etc as a pillow. The weight saving of not taking a pillow are somewhat lost by having a longer mat, a luxury in cold weather and I have a short wide for warmer months but probably wont bother with it now I have this foam mat.

Is this really a techno question or just a gear question?

Probably both but understanding the techno side better, will definitely help in gear selection

[crollsurf]

I got an Onda a couple of months ago but haven't chopped it yet. The plan was to put the 1200mm bit inside the Rsack in 3 folded layers against the back panel and the leftover (width cut to about 45cms from the 54) in the mesh front pocket as a sit pad. Combine the two pieces at night, in mild weather, ridges to ridges, under the shoulder to hip region, for a super light mat. Cold weather- maybe as a safeguard. But the shelter then won't fit in the top of my Rsack! Seemed like a good idea at the time. Still working out the best way to use it. Sounds like you have a good idea. On the snow I suppose you put the flat side of the Onda against your Xlite, in case the ridges allow cold air in and under the Xlite?

The width of the Onda fits nicely top to bottom in the Sonder but yeah, the whole mat takes up a lot of space! I was thinking the pad gives so much padding I'll just sit on my pack. Take it out around camp for a sit mat and then slip it under my bag when I go to sleep. I'm not going to bother with the off-cut unless I'm down the snow at this stage.

[Lamont]

Hey Crolly, It's another world of comfort with two layers of the Onda!
I am thinking I'll carry the 500-600mm piece on top of the Sonder, under the strap. Makes a small roll.
I don't like carrying anything on the outside though. Always worried I'll lose stuff.
"The width of the Onda fits nicely top to bottom in the Sonder"
Yep, that was the thing I checked when I bought it ha ha - but I haven't been using any back padding at all and I thought I would need it so not sure what to do.
By the way, I submerged the Onda in the bath overnight-didn't take any water!
Ships ahoy!

[crollsurf]

Yeah Lamont, not wrong about the double layer of the Onda. Fine with the Onda except for the hip. Being a side-sleeper, once I folded the Onda over to give more hip support, I got a very good night's sleep.

Not sure I like the idea of strapping the mat on top of the Sonder though. One of the joys of UL is being able to crawl under fallen trees without getting hooked up. It does take up a lot of room in the main compartment but I think I should be able to use it as back padding and still find room for everything else.

[Neo]

Pretty sure my pillow is less than 50g. Doesn't even register as a luxury item!