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Which side of a closed cell foam pad goes down?

As I type this, I know it's a very newbie question but I've seen it done both ways (silver side up and silver side down) and haven't been able to find any kind of authoritative answer anywhere.  I have one of the Therm-a-Rest Z-Lite Sol Sleeping Pad closed cell foam pads that intake with me to sit on, rat on, unpack on, keep under my hammock and whatever else I can think of.  It's blue on one side and silver on the other. I usually use it silver side down but have seen others using theirs both ways.  Is there a "right" way? 

10 Replies

Hey @nathanu - Thanks so much for bringing this question to the community! The Thermarest closed cell pads are designed to sleep silver side up.

The blue side is built with a tougher foam to help it handle the wear and tear of the rough ground. The silver side is a bit softer, which makes it more comfortable for sleeping. Its reflective finish also keeps your body heat bouncing back to you. Thanks for asking a great question. Hope you have many nice nights out camping ahead!

At REI, we believe time outside is fundamental to a life well lived.

Ok, so I've been doing that wrong about 1/2 of the time but now I know 🙂  Thank you @REI-CarterC 


@nathanu, now we BOTH know! lol, good question!

REI Member Since 1979

Actually it depends on the brand.  Thermarest recommend silver side up for the Sol and Nemo, recommends silver side down for the Switchback.

I wonder if it makes any difference. As I understand it, the silvery finish reflects radiated heat, while most heat loss is through conduction, which is not particularly influenced by the silver.  The same situation xists with the silvery survival blankets.

I am not a physicist, nor have I played one on TV, so I welcome comments from those more knowledgeable.  I know you are out there....

@hikermorWhich way up is to do with abrasion resistance not the insulating qualities.  At least that is my understanding.

After finding the Which side is up on a Z Lite? post on the Thermarest blog, it looks like their silver side's reflection comes from a ThermaCapture finish.

@OldGuyot, good to know about Nemo brand sleeping pads! Do you know what makes that the case? 

At REI, we believe time outside is fundamental to a life well lived.

"This side is silver because it uses our ThermaCapture finish, reflecting radiant body heat back to you."

They are talking radiant heat, not conducted heat.  I doubt that much radiant heat escapes the sleeping bag, if it gets that far.

@REI-CarterC  As I mentioned above,  I understand it has to do with abrasion resistance.  As I understand Thermarest believe theirs will rub off if is on the ground and Nemo believe theirs protects the foam. 

Possibly Thermarest silver is a sprayed on coating...they describe it as a finish...where Nemo silver seems to use a thermally attached film...part of the moulding process.  Nemo still only claims a R2.0 rating like the Thermarest X-lite Sol but probably Nemo's silver last longer.

Also Nemo use a softer foam on the upper side...the dual foam density you lose some marginal comfort if you use the pad the wrong way up.  The Thermarest Z-lite uses single density so the way up does not affect the comfort.