2mm Underlayment for warming boost

[JTaylor]

Thought I would share a little experiment my wife and I did in Alaska this past winter. We carried sheets of Blue Hawk 2mm underlayment cut to the same shape as our UQ's - 60"x46" to use like insultex - we had the underlayment from my sons scrap pile before we left for Alaska. Im sure any brand would work. Note: what we experienced may not work for everyone else!

Our winter UQ's are made from 7.5 climashield which does just fine to 0 degrees for us - we're warm sleepers. Anything below that made us chilly especially if the wind was blowing hard. With the sheet of underlayment between the hammock body and the inner side of the UQ, we could get to -20 fairly comfortably - we also used nalgene canteens filled with hot water. We could manage at least 4-5 hours of good sleep and then we would dump the now just barely warm nalgene bottles over the side and doze another few hours. Our top quilts were 10 degree climashield sleeping bags.

We checked for any sign of condensation build up after every use. A couple of times we had a little dampness on the hammock bottoms, but nothing that didnt dry out fairly quickly - we had on merino 250 wool undies. Humidity was fairly low, but we also tried the sheets between 30 and 40 degrees and had no problems. Actually, it was too warm to use the sheets above freezing - simple enough to pull the sheets out and go back to sleep. We did try the sheets between us and the hammock and we both ended up with wet backs very quickly. As far as I know, the underlayment acts as a sheet of plastic - a very thin sheet of plastic with a very thin piece of foam sandwiched together, but for some reason allowed us to stay comfortable enough to get some decent sleep - without getting wet. Im sure just acting as a wind blocker helped more than anything. We had the foam side toward the hammock bottom.

So - Im sure ymmv, but in really cold weather we will be carrying a sheet of underlayment. This stuff is very light. I think our sheets weigh less than 3 oz.

End of report.

JT

[JTaylor]

I forgot to add that we both used UQ protectors made from breathable 1.1oz nylon also on snowy or rainy nights.

[Phantom Grappler]

Thanks for successful cold trip report. Is underlayment used in home construction?

[JTaylor]

Thanks for successful cold trip report. Is underlayment used in home construction?

Hello Phantom! Its used for wood floor installation. I have gobs of scraps from my sons business - if you want a sheet I can pop some in the mail for you. Stores like Lowes and Home Depot have it. Its surprisingly robust - made one sheet last the entire time (still have it in the hammock stuff). Be warned - a roll is like $30 at the big box stores.

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JT

[TominMN]

Thanks for successful cold trip report. Is underlayment used in home construction?

This is thin foam that is typically installed under free-floating, engineered flooring such as Pergo.

[JTaylor]

This is thin foam that is typically installed under free-floating, engineered flooring such as Pergo.

Exactly. Thanks TominMN!

[Phantom Grappler]

Me too, thanks Tom

[BillyBob58]

Thought I would share a little experiment my wife and I did in Alaska this past winter. We carried sheets of Blue Hawk 2mm underlayment cut to the same shape as our UQ's - 60"x46" to use like insultex - we had the underlayment from my sons scrap pile before we left for Alaska. Im sure any brand would work. Note: what we experienced may not work for everyone else!

Our winter UQ's are made from 7.5 climashield which does just fine to 0 degrees for us - we're warm sleepers. Anything below that made us chilly especially if the wind was blowing hard. With the sheet of underlayment between the hammock body and the inner side of the UQ, we could get to -20 fairly comfortably - we also used nalgene canteens filled with hot water. We could manage at least 4-5 hours of good sleep and then we would dump the now just barely warm nalgene bottles over the side and doze another few hours. Our top quilts were 10 degree climashield sleeping bags.

We checked for any sign of condensation build up after every use. A couple of times we had a little dampness on the hammock bottoms, but nothing that didnt dry out fairly quickly - we had on merino 250 wool undies. Humidity was fairly low, but we also tried the sheets between 30 and 40 degrees and had no problems. Actually, it was too warm to use the sheets above freezing - simple enough to pull the sheets out and go back to sleep. We did try the sheets between us and the hammock and we both ended up with wet backs very quickly. As far as I know, the underlayment acts as a sheet of plastic - a very thin sheet of plastic with a very thin piece of foam sandwiched together, but for some reason allowed us to stay comfortable enough to get some decent sleep - without getting wet. Im sure just acting as a wind blocker helped more than anything. We had the foam side toward the hammock bottom.

So - Im sure ymmv, but in really cold weather we will be carrying a sheet of underlayment. This stuff is very light. I think our sheets weigh less than 3 oz.

End of report.

JT

So, is this underlayment a vapor barrier(VB)? I suspect it might be. If so, it(a VB) is part of the secret of the Hennessy Hammock Super Shelter(HSSS) IMO, where a 2 oz space blanket is placed between the hammock and the under pad and the other(outer) VB, the undercover of silnylon. Works like a charm for me and a few others. Also, on and off for 30 years but a lot more frequently in recent years, I have used VB clothing to boost whatever gear 20+ degrees, plus keeps my insulation bone dry. If this underlayment is a VB, then I am not surprised you got that kind of boost. As a VB stops evaporative cooling(think swamp coolers and ACs) 100%, and prevents body vapor from condensing in and dampening our insulation. Thanks for sharing!

[JTaylor]

So, is this underlayment a vapor barrier(VB)? I suspect it might be. If so, it(a VB) is part of the secret of the Hennessy Hammock Super Shelter(HSSS) IMO, where a 2 oz space blanket is placed between the hammock and te under pad and the other VB, the undercover of silnylon. Works like a charm for mend a few others. Also, on and off for 30 years but a lot more frequently in recent years, I have used VB clothing to boost whatever 20+ degrees, plus keeps my insulation bone dry. If this underlayment is a VB, then I am not surprised you got that kind of boost. As a VB stops evaporative cooling(think swamp coolers and ACs) 100%, and prevents body vapor from condensing in and dampening our insulation. Thanks for sharing!

Thank you, BillyBob58. I asked my son about it a bit more and he says it is a vapor barrier. I love this stuff. Our winter jackets and pants were VB also.

[psyculman]

Thank you for this information. It adds some useful insights for cold weather trips.