Styrofoam insulation -- foil in or out?

[BetaB4]

I have two exterior cinder block walls in an apartment that are being redone on the inside. The furring strips are in place and the walls will be getting sheetrocked. I have 1-inch styrofoam insulation that will be going in the spaces between the furring strips. The styrofoam insulation has foil on one side.

Which side should I keep the foil on? -- the inside facing the room, or the outside facing the cinder block wall?

I'm thinking the inside since that's the "warm" side, but I don't know.

[RicodJour]

An excerpt from

this: "All radiant barriers have at least one reflective (or low emissivity) surface, usually a sheet or coating of aluminum. Some radiant barriers have a reflective surface on both sides. Both types work about equally well, but if a one-sided radiant barrier is used, the reflective surface must face the open air space. For example, if a one-sided radiant barrier is laid on top of the insulation with the reflective side facing down and touching the insulation, the radiant barrier will lose most of its effectiveness in reducing heating and cooling loads."

The foil radiant barrier requires an air space - it's not supposed to touch anything. If it is touching the back of the wall covering it loses some of its effectiveness.

The foil also acts as a vapor barrier, which may or may not be necessary depending on what type of rigid foam insulation it's on.

R

[ransley]

I bet both sides have foil but one side is painted as my Celotex board was, try alcohol or laquer thinner or some paint remover to see. One inch is only R 7.2". 2" is still substandard in most zones for R value, I used 2-4.

[BetaB4]

Thanks. I checked out the link and read the article, and I appreciate you providing the key excerpt. I had tried doing some Internet searches before posting my question but didn't seem to get to any sites that had the information I wanted.

The bottom l> >> I have two exterior cinder block walls in an apartment that are

says this:

[RicodJour]

What color is the foam? I'm curious as I haven't seen rigid foam insulation with foil on one side.

R

[BetaB4]

[RicodJour]

White foam is polystyrene. The typical expanded polystyrene stuff (Styrofoam being the biggie in brand names) is made up from little beads of polystyrene bonded together and used in everything from packaging to coffee cups. It has one of the lower insulation values of the rigid foam insulations - something around R3 or R4 per inch.

More info at:

R

[BetaB4]

It definitely looks like white "coffee-cup-like" polystyrene, with foil on one side. I'll get the exact brand name etc. and post it.

[BetaB4]

Here's what it says on the 4x8 sheets of insulation:

"Polyshield" Sheathing/Underlayment

ICC ESR-1820

Cellofoam North America, Inc. Conyers, GA

Here's their website:

[ransley]

That site crashes my IE. Polystyrene is white and only maybe R5 new

4.6 settled. Polyisocyanurate is white, [not as bright] and is R7.2 new and settles to R 6.8 or so, it is superior in R value for spaces with little depth. 1" or even R 10 is not much on an exterior wall, unless area is moderate temperature.

[EJ]

replying to ransley, EJ wrote: home depot sells one sided foil foam sheets in the store. One side is foil, the other side is thin plastic. we are using it for outdoor feral cat boxes.

[hubops]

.. this guy might know :

[excccel]

replying to RicodJour, excccel wrote: mine is white, R-tech by Insulfoam