I'm boxing-in several pipe drops in the corners of rooms. The pipes drop
vertically and then exit horizontally to go to a radiator. I'd like to
find a way to fill the gaps around the horizontal pipes, where they exit
the boxing, in such a way that the pipes can still move slightly without
making a noise; the boxing will be covered in lining paper and then
painted.
Ideas so far include soft rubber or a squirt of expanding foam (trimmed
back flush), but there must be a better way. What have others used?