Plastic Under Lid?

When you guys incubate your eggs do you but plastic on under the Lids or do you just put the lids on? I know that Ralph Davis puts plastic under the lids but I didnt underdstand why.

Lids are not completely air tight. Plastic wrap keeps things sealed in for the most part :)

Press n Seal under the lid

Saran wrap on every clutch for me. As Heather already states, it helps keep the humidity in, and keeps the substrate from drying out.

We used the Press n Seal for this year (our first year with eggs) under the lid. Seemed to work beautifully. We've been giving the eggs a quick air out every 3 or 4 days and daily after day 45 until I do the first cut on day 52 (and gawd I'm nervous of that LOL).

I use 3 gallon plastic pails that come with pretty tight lids, and after 3 years using them on multiple clutches I've never had any problems, nor have I had to add any water during incubation. If, however, I were using, say, standard plastic sweater boxes or something similar, I'd definitely use the plastic wrap!

i have been testing my incubators for a few months now and have been getting a little too much condensation because the rubbermaid egg boxes arent air tight enough. i added press and seal under each lid of each egg box and now i only get a vey fine mist of condensation which, from everything i have read, is not bad.