The ventilated polystyrene cover features four ventilation portals, each with a finger-set polystyrene block so that you can open as many of them (or none) as you wish. (Please note that, once removed, the blocks are loose and can go missing.) The cover itself has a depth of approximately 1 3/4", making it an ideal place for emergency winter feed (ie. sugar bricks, mountain camp method, winter patties, etc). On the other hand, we advise using the accompanying mylar inner cover during all other times of year to avoid excessive burr-comb build up within the cover cavity.
Also included is a clear mylar inner cover which features small ventilation notches (see attached images).