It's a big zipped square bag.
Covers the whole Fast Ferment conical, stand and airlock.
If you put a heater in the beer it make sure that you're not heating the shed or brewery by keeping the heat in.
If you need a brew cooling you put those big 2 litre plastic bottles full of frozen water in there.
Each 2 litre bottle of ice will drop the temp by 5 degrees f for 24 hours..
There's handy velcro openings to see the thermometer ..
It's a useful bit of kit, make sthe conical look really tidy too!