Digital BW, The Print

I am looking to find out what the GSM thickness rating is. How does
the GSM rating compare to mm thickness. For example, how many mm is a
paper with a GSM of 255? How many GSM is a paper that is 1.3 mm? I am
also interested in finding out the maximum thickness of papre an Epson
2200 will handle. Thanks a lot and I appreciate any response. Steve