Just purchased two colonies from a former commercial Beek. When I arrived to inspect the colonies I noticed a hive top spacer with a plastic sheet hanging out. Initially I though hive top baggie feeders, but upon further inspection I noticed it was just that, a sheet of plastic, with a piece of 1/4" Styrofoam insulation and then a transport cover. When I asked about the purpose he indicated that it helped keep up the brood temp and humidity. I have never seen this although I do have limited experience and there are a lot of things I have not seen. Has any one ever seen this or tried this before. The colonies are healthy. It is my understanding that it is generally practiced to increase ventilation not decrease it.
In the end, I understand the bees know what is the best climate inside the brood chamber and will adjust accordingly.
Thanks for the feedback.