The Reynolds Oven Bags are made with a mix of heat-resistant nylon (from their FAQ on the website). I think this is FDA approved to be food-safe up to 400degrees. I don't typically use the FDA's approval as my "safe" guideline.
I did a search on this and found some blog talk from some website that cites research (see below). I tried to look at the research from the "Journal Material, Sci. Letter" link and could only see the beginning of the paper.
Looks like "polymide 6,6" is the nylon and produces toxic derivatives at certain temps over a certain time.
Without digging deeper, I see that there may well be credible research out there that shows that this stuff may not be a great choice. Sure there are lots of not great choices out there (teflon, etc), but I'm choosing to skip this one.
Dorado-Rodelo et al, Effect of ovenproof plastic films on the quality of spotted rose snapper fillets during frozen storage, Packag. Technol. Sci. 2007 (specifies Reynold bag material)
Soto-Valdez and Gramshaw, Cyclopentanone and cyclopentanone derivatives as degradation products of polyamide 6,6, Journal Material. Sci. Letter, 2000
hmw0029 at 1:24PM on 12/15/09
@hmw0029: Thank you. I appreciate your research effort and though I probably can't access those journal articles without a subscription, I'll check things out on Google Scholar to see what else I can find.
Susquehanna at 1:38PM on 12/15/09
Yep.
Both article abstracts from the Journal of Material Science Letters and the one from Food Additives and Contaminants confirm that volatile compounds from nylon oven bags migrate into food.
Susquehanna at 1:56PM on 12/15/09
Ah, wait - the first article hotlink above was cited by hmw0029 and confirms that nylon cooking bags emit volatile compounds.
The second article hotlink is one I found on Google Scholar and confirms the migration of volatile compounds from nylon into chicken. It also suggests that the amount of VOC "can be" assumed to be harmless. Right, right.