We have just removed the carpet from our house (as we are planning on wood / tile) and have salvaged most of the underlay which is used (obviously) but actually pretty good quality and could be used again for e.g. smaller rooms (single bed) or cloakroom / utility room / office / shed / outhouse etc
I don't know the exact dimensions but there is a lot and it is FREE (as long as you come and get it from Catford, near the station) - we took it from two reception rooms and two double bedrooms.
Call Sarah 07972 368 261