100 gram quality is thick and fabric like. They can be used over and over again. Because they are so heavy, they require more securing tools like tacks or staples.
40 gram quality is thinner than crepe paper but thicker than tissue. They are usually only good for one time use. They are light weight so they hang easily with tape or glue dots.
Fringe quality is not lost in the 40 gram! This is Frolic and Frills favorite!