Hi Aidan,  We use coffee filters (the square kind, for percolators) that have
been cut to size, for wrapping small biopsies and bloody specimens.  The
trick when embedding is to keep the cassette with the paper inside as warm as
possible so that the paper does not harden.  In other words, if you use an
embedding center that has a holding chamber, keep the cassettes in the
holding chamber (preferrably filled with paraffin) just until you are ready
to embed them. Don't allow them to get cool so that the paper inside
hardens--you'll have a time trying to open the paper!!  We also have nylon
embedding bags (Shandon) that are used for small specimens and curettings.
Good luck!!       Jeanne Godine
                                           Pathology Consultants