If you put the foil side "against the sheathing" then the
heat will conduct from the roof to the foil.

You could put the foil side under the rafters, facing in the
direction of the sheathing. It would also be a lot easier to
install, you don't have to cut the foam to shove it in
between the rafters.

--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


"1D10T" wrote in message
news
With the foil-side up it reflects the radiant heat. Perhaps
I wasn't clear,
or you're not familiar with the product - the foil adheres
to the Styrofoam.
I believe it's often used under vinyl siding.

"1D10T" wrote in message
...


1" Styrofoam, backed with aluminum foil, foil side up,
against the
sheathing. Cut it into strips, making a snug fit pressing
them between the
rafters. Available in 4 x 8 sheets. The white Styrofoam
will
look good too.