Every professional faux finisher needs a portfolio of sample boards.  I have tried many different products and have finally settled on Polystyrene.

Why?

Cardboard and paper based boards are inexpensive and easy to purchase but they dont stand up well to wear and tear.  My corners would fold over and did not present a professional look.  I finally found polystyrene from my local plastic supply company.

I have boards over 6 years old that look as if I fauxed them yesterday!

The boards are a bit more expensive than cardboard at about $2 a piece but I feel it is a small price to pay for a high quality look.

I use these boards to practice my finishes on.  If I don't like the finish I re-use the board.  Paint and venetian plaster stick to the plastic.