In response to Paul Eggert's query, a Teflon ironing sheet is a thin
flexible sheet made out of woven Teflon.  The ones I have are about
30 cm by 20 cm, or 12 inches by 8 inches.  These sheets are used by
sewing enthusiasts and patchworkers for applying applique patches
to whatever.  They cost a few dollars; any craft or sewing shop should
stock them.

John Phillips in Hobart, Tasmania