From Lab Society:
NEW, WITH A SILVERED VACUUM JACKET.
The all new Packable Distillation Head (PDH-2S) now has a silvered vacuum jacket, which allows increased thermal retention. The vacuum jacket wraps around the column and helps keep heat from escaping.
INCREASED THERMAL RETENTION.
The increased thermal retention allows heating mantles to use less electricity, as the vapor will stay a more consistent temperature.
Having a consistent temperature during fractional distillation is highly recommended, so you can accurately distill compounds at their correct temperatures.