Did I find a lighter, cheaper alternative to the GG Thinlight Insulation Pad 1/8″ ???

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

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