On 25/01/2010 08:10, Nightjar "cpb"@ insertmysurnamehere wrote:

The theory with fibre washers is that water leaks down the thread to
them, they get wet, swell and seal the connection. The theory with PTFE
tape is that water does not leak down the thread to begin with.

Colin Bignell

Er, I think you'll find that in a tap connector, the fibre washer stops
water leaking down the thread.

The water in the pipe is in touch with the washer, which swells and
stops water getting to the thread.

PTFE tape just seals the thread up, or doesn't as the case may be ;-)