I'm asking because I've never seen or used one:
http://gossamergear.com/sleeping/1-8.html

I have no idea what they feel like, how cushy, how much insulation or how durable they area. I'd like your opinion about the following, to compare and contrast....

When I put my floor in, I had extra underlayment. Specifically Quick Step Combi Floor Plus:
"This unique, three-in-one underlayment offers improved sound-absorption, moisture protection and embossed self-leveling."
http://www.mjflooring.com/products/laminate/quick-step/

I squared it off by eye and came out with this piece:
I

The GG Thinlight 1/8 specs are:
19 3/8in x 59 1/8in x 1/8in
high end weight: 92g

The Underlayment piece specs are:
61in x 26in x 1/8in
measured weight: 106g

By my calculations...

GG:
0.080310986 grams per sq in

Underlayment:
0.069508197 grams per sq in

Can someone check my math? Also, anyone that has used the GG piece and handled underlayment, can you compare?

When laying on my hard, hard, laminate floor with this stuff under my back, it actually makes a noticeable difference. *shrugs*

Thanks!

Your numbers seem correct. The floor underlayment foam sheet is LDPE foam with a plastic film facing. It's very light, but it has about 1/4 the insulation value of the Evazote (EVA) foam that the GG thinlights are made from.

The Evazote foam has an R-value of about 3.9 per inch, or roughly 0.5 for the 1/8" thickness, whereas LDPE foam has an R-value of about 1 per inch, or 0.125 for a 1/8" thickness. The cells in the LDPE foam are much larger and less numerous than those in the Evazote.

You may be familiar with Insultex. It's a material used by some UL hammockers for MYOG underquilts. It has a bit of a cult following. It's just LDPE foam sheet, like the floor underlayment, but with nonwoven polypropylene scrim on both sides instead of a plastic film face. The company that markets insultex makes a lot of outlandish claims about it's performance as insulation.

Thanks for the info Colin.

Perhaps then the underlayment would only be suitable for a warmer season or two if someone wanted to realize the weight savings.

By my calculations, I'd save 15.83734211g/0.56oz with the underlayment (assuming you own one of GG pads on the heavier side.)


I have heard of insultex...my buddies use it in their hammocks. I'll have to ask them their thoughts.

Colin,

My googling suggests a higher R value for the underlayment, given the R value of this comparable(?) underlayment:

foam underlayment


Wouldn't the R value per inch of thickness be something like 4.66(1/.06" X .28R)?

Not real sure of my logic so I invite feedback/clarification.

Daryl

Edited by lyrad1 on 06/16/2011 12:23:06 MDT.

Bryce,

I bought a roll of similar stuff a while back but haven't done anything with it yet. I like the looks of it.

I see some other underlayments that have mylar on one side and the foam appears to be of a finer texture.

I also recently bought a package of small foam sheets that have adhesive on one side. I figure I could stick them on things like the heat shielding tiles that are placed on the space shuttle.

I like foam.

Daryl