[cperciva]

Not necessarily -- at least, not unless you count people reusing discarded rubber bands. Typically the strategy used in cases like this is to make the material break down faster in the presence of water; assuming postal workers aren't trying to get the mail wet, the rubber bands should also stay dry enough to be reusable.

I have plastic compost bags which stay intact for months in the cupboard but fall apart in 2 days when filled with wet food waste.