When you are talking about sewing pattern paper it could be one of two things. The first you’ll most likely be familiar with, it’s the paper a purchased pattern is printed on. The pattern pieces (I.e. bodice, sleeves..etc) and their size lines will be printed on either a tissue or white paper. For Experimental Space patterns, your pattern will be printed on thick white paper. It is much less likely to tear, more durable to do alterations like FBAs, and generally lasts longer.