Working in a trade school I had access to many different types of materials.  Metal formed very easily, but the environment of a shop got banged around leaving openings around the filter which would leak.  Plastic solved that problem and as I said reduced the number of times hands and wrist were cut.  Out in the field we also found cardboard a good one time substitute.
	
		
			
		
		
	
			
			
				
	