Do you know what the defined RSI rating means? I have heard so many
definitions that none of them make sense anymore. Many try to equate
it with the R factor unsuccessfully and I believe it has something to
do with "reflective..."

"daestrom" wrote in message
...

"Solar Flare" wrote in message
...
Isn't the reflective surface only effective if there is an air gap
next to it?


That's my understanding. It reduces the amount of heat transferred
across the air-gap by radiant heat transfer.

Since convection is the larger heat transfer mechanism for heat flow
upward (such as in an attic in a cold climate), they are not as
effective when trying to stop heat loss. So you usually only see
them touted in situations to stop the heat flow downward. Such as a
hot attic to an air-conditioned space, or from a heated room
downward to an unheated crawl-space/cellar.

I have read some testing reports that show those 3/8" doubvle
radiant barriers under slabs to have a non-measureable difference
to no insultaion at all. ****ed off my concrete guy but I gave him
a print out of the report and now I can't find it again.


Yeah, putting some other material in direct contact with the foil,
such as a layer of wallboard, or a concrete floor pretty much
nullifies the affects of the foil. Of course, if the foil is over
one inch of foam board, you still have the one inch of foam and its
insulation value. But not worth paying any extra to get the foil.

daestrom