First, make two barrels, one big and one small, then put foam with a certain thickness in the big barrel (that is, the combination of white particles inside when loading things, and make small particles when putting them into the big barrel), then put the small barrel in, ensure that the position of the small barrel is centered as far as possible, then fill the foam between the big barrel and the small barrel, and finally seal the upper edges of the two barrels to prevent the filler from exposing. It's such a simple heat preservation.