Cels tend to stick on rice paper. Though, it is a 
good cushion between cels and genga during 
storage. It is hard and messy to remove them once 
the cel sticks.

I believe cel will stick to glassine too. And 
would be tougher to remove since it is sturdier 
than rice paper. Possibility of paint loss is 
greater when using glassine since it does not 
tear easily, it would have mean to tear off part 
of the paint at which it sticks. Again, it 
depends on the condition of storage and the state 
of the cel. ^^

I use PP (polypropylene) to back my cels. It is 
transparent and I wouldn't have to worry about 
cels sticking onto it. The fact is, I don't plan 
to separate them if it starts to stick. Anyway, 
it's transparent and it wouldn't affect how the 
cel would look during scanning even if it does 
stick. Individual preferences.