This is officaly one of the Puffle Hats. The Propeller Hat is also a toy and is also a item. The Green Puffle's wear this item as the toy. Some other penguins might want to match their Green Puffle, so they wear the Propeller Cap. which is not noted as hat in the inventory though. You can get this from the catalog. It is very likely that only the green species will wear it. though some others like it too.
Aunt Arctic's puffle with the Propeller Hat.
A unknown puffle wearing a Propeller Cap in the sky.
Another unkown puffle carrying a hammer with a Propeller Hat.
Small picture of a green puffle with a Propeller Hat.
Big picture of a green puffle with a Propeller Hat.
In Jet Pack Adventure, you appear with your penguin and a puffle wearing a Propeller Hat if you have a green puffle.
Too many of these already. An unkown puffle with a Propeller Hat.