Menthol adds a flavoring agent, not fiberglass. Reds are the normal full strength smoke. "Lights" are for almost every brand the same tobacco put into an aerate filter. Filter draws in air from side of filter thereby diluting cig smoke. Of course the joke on the smoker is that the air holes happen to be where you hold the cig. Tar and nicotine
test levels are determined using a machine that does not cover any holes. More recent tests are showing no diff in cancer rate etc between reg and light smokes since apparently light smokers draw it in to lower part of lungs.