Can I use starch on crochet - acrylic? Or how to stiffen coasters?

[MassiveBumperlicious]

I'm making some heart shaped coasters for part of a wedding present, but they are a bit thin an curly. Can I use spray starch to stiffen them, even if they are acrylic? I guess the only problem is it will wash out if the coasters need washing. How else could I make them stiffer?

Thanks butterfly, have sewed felt on and they look rather nice even if I do say so myself! Good tip