Someone wrote:
No fabrication necessary. Just get a filter that the vac originally
came with. The foam is not it. The foam piece is supposed to go over
the pleated paper filter.

There are also washable pleated filters for most models. They are about
$30 but last a long time.
..
That's odd; the paper filter on mine goes 'over' the foam which
supports and prevents it from collapsing inwards into the sort of
basket thing below the motor????? Paper filters clog rather easily;
e.g. plaster dust etc. Just thought I'd ask?