stuart noble wrote:
Jerry Built wrote...
I'm contemplating using Mighton plastic parting bead to
partially draughtproof some sash windows, and stop them
rattling. Has anyone used this? The problem I have is
that the bead is supplied in lengths of 2.4m and 3m,
neither of which work well with these windows - there
will be maybe 40% wastage, unless I can join lengths.
So: can lengths be joined, and how? Any other helpful
information will be very welcome.

Can't really see the benefit of plastic,

Have a look at Mighton's site. It's not a plain plastic strip
with a rounded nose like timber parting bead, it's more like
a broadarrow in section: