Using a blanket as temporary insulation

I didn't insulate my hives this winter and so far my two hives are both alive (knock on wood). However, I've been told that bees are raising brood now and won't form a winter cluster if it gets cold, making it more likely for them to die.

I don't feel like going out and buying sheet foam, especially because one of the hives is overwintering in a single deep and will likely be in two deeps next winter, meaning I'd have to get new sheet foam and recut it to fit the hive next year.

So can I just strap some blankets around each hive? I don't mind drying them out and replacing wet blankets with dry ones when it rains. I won't need insulation for much longer. And at what temp do they need insulation? If it's above freezing I don't need it right?