I have 6 1928 $1 silver certificates, one of which is the special paper note pictured. There are variations due to overall quality of the notes, but I would never have guessed that the paper is different. Looks exactly the same side by side. Below is a close up with my digital microscope of two notes side by side. One is just slightly dirtier than the other. Maybe not super useful since I had to edit it down to 300kb.