You would think the 100 micron would be thicker but it has to do with the pore size, not the thickness. This is another reason 100 micron socks clog up fairly quickly - less material.
Adding filter floss is a great idea to make your filter socks last longer between changes. Filter floss will trap large to small debris before it gets to the 100 micron filter sock.
The material of our filter socks is woven therefore you can calculate the micron size. Filter floss is bulk random fibers making it impossible to give a consistent micron rating.