The seedlings were already planted in the cups. With the heater running every now and then, they were drying out. I have been misting them every evening with a spray bottle, but that was getting old. So I trimmed the first 1/4 inch off the rim of some more cups and cut little vent holes in the bottom. Then flipped them over and stuck them over the seedlings. It is much warmer up there on the shelf by the ceiling in the laundry closet.