I took a class a long time ago from Omnigrid rep. She had us cut with different size rotary cutters. I found I liked the 18 mm size the best. I had more control and no problem at all going through four layers of fabric. And the blade are much less expensive. I liked the Clover brand the best for the small cutter. I do use the 45 mm but when I go back to the 18 I wonder why I have the 45.