I am getting ready to recover the tops of 2 coldframe lids and am wondering about the best material to use. The coldframes are made from 2 wooden box shaped frames that were going to be tossed until my scavenger husband spotted them. Last fall we covered the sides with plastic sheeting, leaving the top and bottom open. My husband then framed two lid-sized retangles which we also covered with the plastic (cheap Walmart type). We set the open bottoms onto our raised beds, surrounded the north, east and west sides with straw bales, and raised the most fantastic lettuce and spinach through the winter that I've ever eaten. The sides are still intact, but the plastic on the lids has fallen apart through the summer (weathering I'm sure), so they need to be recovered. I now have all kinds of tiny bits of falling apart plastic in my beds, which is kind of unnerving me, and I'm wondering if it will cause any problems, toxicity-wise to the soil in there? I'm also wondering what is the best thing to recover the lids with. I probably won't worry about the sides till next spring as they're still intact, but I do need to find out what the best materials would be that aren't too expensive. Any ideas would be appreciated. One box is about 6'x3', the other about 5'x4'. Both are just under 3' deep.
We use plastic to cover our greenhouse. The difference is probably the grade; it is 6 mil (I'm assuming that has something to do with thickness or the type of plastic) and carries a 4 year warranty on it. I would say you might be able to get some smaller squares of it if there are any professional greenhouses around that have some scraps. But I definitely would not want the plastic in my garden soil. Although I don't know if it is actually toxic, if it ain't good for growing in, then...
What I've often seen for cold frames is discarded window frames that still have the glass intact. I have half a dozen in my garage, should you ever come to Tennessee! But you can probably find them on your local www.freecycle.org or Craigslist, etc. Also look for houses being redone.
Thanks for the thoughts, and actually I would love to take off and drive to Tennessee for those windows, but I'm afraid my schedule won't allow. I think the plastic I used was 4 mil, and I used two layers, but maybe if I used a heavier grade and something with a warrenty, then at least I could get it off and changed before it started to crumble. I'm trying to pick up bits and pieces, but they just want to crumble further. I will check the sources you listed for windows. I just figured it would be hard to find dimensions that fit my boxes. Glass would definitely make it more stable though.