I like printing my foundations from the computer so I had been using regular copier paper. I found it was stiff and I didn't like the punching noise that the needle made as it went through it.
I have since been using pads of tracing paper I bought at my local dollar store. 9X12 sheets , 40 sheets for a dollar. I also use HILROY plain writing tablet (ID#35700) 8X10 sheets, 100 for about 2.50. The thinner paper runs through the printer fine and I can bend it much easier and it has a much more pleasing piercing sound!!