you could use also cardboard.

 

It doesnt really make a difference I dont think with metal fans. Nor do I know what models of vehicles have plastic fans, but when you put a winter front on anything with a plastic fan make sure you have 1/3 of the radiator surface area open, and it needs to be 1/3 evenly. Preferably on a pickup put the winter front right on the radiator. The plastic fan catching air in one place can tweak it and could cause it to break. With pieces flying who knows where. Metal fan, I dont think its going to shatter because of tweaking.

 

Cardboard seems to be the most popular method it seems
Edit: I think people usually put the card board/whatever just behind the grille, idk if the gap between the ac condensor and the radiator is suffecient enough to stop the tweaking plastic fans in such as a electric setup, never thought of that.

 

thats because it is very cheap if not free

 

If i were to make one I thought of somin along these lines: