plastic or copper ball just curious

[breezer]

i was in a plumbers merchant and they had a football size copper ball for a float valve, (it really wwas a copper float, not a football)

but no one could tell me why the copper ones are big, (apart from they are made that way)

so my question is, is there any advatage of a copper ball over a plastic ball for a float valve (apart from price, but if that is true, why is the bigger one copper)

 

[kevplumb]

dunne breezer
it's just always been like that never seen a 1"" valve with a plastic float

 

[breezer]

oh