Drawcord footboxes have developed a reputation for being cold, but I feel it isn’t necessarily a shortcoming that is inherent to drawcord footboxes, but a shortcoming that is inherent to a certain design of drawcord footbox that happens to be the most common. The end drawcord. An end drawcord pulls the surrounding down in, but the center is left as a cold spot of nylon and cord. You can stuff a sock in there to make sure there is no actual air transfer, but you can’t really get away from the lack of insulation in the center.
This shows a big cold spot pooping a sock……
Set the drawcord back and add a draft collar and it’s pushing the down together to close over the opening with thick loft and form a round footbox.
These pictures below show a bunch of insulation pushed together and sealed with a draft collar, forming a nice warm circle.