I just built a greenhouse using the 3 mil Solexx (see pic link below). While I haven't been through a season with it, I'm pretty happy with it so far. Easy to install, looks nice, and the snow slides right off. I also like how evenly it diffuses the light. While I don't have enough experience to compare its heat retention to other glazings, its advertised R-Value, 2.0+, is pretty competitive.

I found a local guy that was selling it in custom length rolls, so I just purchased a big roll instead of the individual panels. A little cheaper, and easier to install. I opted to overlap the panels rather than use the H-Channels to connect them.

It is important that you seal the fluted ends to both trap the air for insulation and prevent moisture from getting in. While they instruct you to squeeze caulk directly into the ends, I found this VERY tedious, difficult, and incomplete. A much easier method is to FILL the U-Channel trim that goes on each exposed end with caulk, and then simply push that onto the end. This fills the individual channels much better, and it alot faster.

Here is a link that might be useful: Solexx Greenhouse

The page at the following link has a nice chart comparing the R value of Solexx panels with other greenhouse coverings:

http://www.solexx.com/greenhouse_coverings.html

I have a Solexx greenhouse which I do not heat and only use during the daytime - I bring my plants indoors to a heated sunroom at night. For the way I use my greenhouse, I'm very happy with the Solexx. As long as the sun shines the greenhouse heats up nicely to about 80 degrees on the coldest winter days. On cloudy winter days I do need a small heater to boost the temperature. But at night the greenhouse quickly drops to match the outdoor temperature. I do agree that the light diffusion of the Solexx is terrific. I'm in Colorado with strong high altitude sun which can easily burn plants and I think Solexx is the perfect covering for my situation. Even on overcast days, the greenhouse is very bright.

I would suggest you search the posts for how other greenhouse users have insulated their greenhouses both inside, outside, and even underground. Folks here have mentioned all kinds of insulation methods ranging from simple things like bubble wrap, styrofoam, hay bales, and water tanks, to more involved things like underground insulation and underground heating cables.

Dorothy

I have 8mm twinwall and my R- is 1.57. If you want more than that you'll want another layer with an air gap in between, and you'll likely get ~R-2.5-3.0 -ish. I'd insulate the north side and forgo glazing.

Dan