Hi guys..I've been away a long time, back again.. ;) We built a house years ago, and ended up selling. We're looking to build again now & it's interesting to see how things have changed. A builder we met with was telling me about an "insulating mat" you can put under the basement slab that does a good job. After a little research, I think he's referring to "ecofoil". On paper it seems like a great product - much cheaper than rigid foam ($900 or so for a basement) and R3. Just wondering if anyone has experience with it, and if there are any "cons" to using it. thanks in advance!

I googled "ecofoil" and found aluminum sided bubble wrap. Is that it? Might be OK for a vapor barrier (??), although poly is likely a good deal cheaper, but for insulation, stick with EPS foam - 2" or 4". You get what you pay for.

yes, that's it - basically industrical strength bubble wrap. The builder we talked to is definitely well-regarded, has been around a long time - he said the stuff is great.

I don't know the material - it may be the greatest bubble wrap ever made; it's just not what I would consider insulation. Of course it depends on where you are; maybe it's OK in Arizona, but it's also nowhere near enough insulation if you are in a cold climate.

I've had various salespeople peddle this stuff for years claiming it is "radiant" under slab insulation. Hogwash. It's snake oil and in my opinion worthless. Stick with EPS or XPS (not as environmentally friendly as EPS) and put in more than you think you need. This is a location you will never have access to again. I am in zone 5 with very high humidity and used 4" of XPS under the slab (code requires 2"). It cut the condensation and basement dampness to about zero.

Are you planning on heating this slab? If so R3 is not nearly enough. If not heating, why even bother with this supposed R3? Just heavy vapor barrier and be done with it.

Do not use foil underground, there is no such thing as a radiant barrier underground. The Barrier™ under concrete thermal insulation and vapor retarder product family is a high-performance, simple to use and labor saving product for all of your under-slab, under concrete, and radiant floor insulation projects. The Barrier's™ unique core material is an expanded polystyrene (EPS) with a jobsite tough, heavy-duty poly film laminated on both sides. Adding to the Barrier's™ labor saving features, it has a 3" flap of film running down the sixty-four-foot length of the Barrier™ insulation with an aggressive double-faced adhesive on the opposite side of the overlap -providing a seamless vapor barrier. Also protects against Radon. FMI see http://www.barrett-inc.com/thebarrier.php

" If not heating, why even bother with this supposed R3?"
I have a cold basement; ever since I installed mini splits upstairs, and tossed the furnace, there is nothing making heat on that floor, so it stays in the mid 50's through the winter, which is a several degrees above deep ground temperature. My insulated floors stay at room and wall temperatures, except in the few uninsulated spots where the temp is 3-4o lower. So not a huge difference, but 3o in this environment is welcome. If/when I decide on a heat source and the surface temps increases, the difference will be greater. Yes, insulation makes a difference.

Oh I agree, insulation will effect how the space holds heat. But how much insulation did you put under your slab Bob? I guess it depends on what you are going to use the space for. But my point was that if you are going to insulate, put some meaningfull insulation under there. Is R3 better than nothing, well yes, but not much. And is this stuff ever going to reach or sustain an R3 over time?

My basement has a garage and storage, but I put 2"/R10 under the slab so if I want to heat those spaces, it will retain heat pretty well(walls 8" ICF at R30ish). As mentioned, if you think you are going to want to heat down there, it is way easier to put it in before the pour