These broad-tipped markers have the ability to make thin or wide lines depending upon how you hold the pen tip when you write. This can be useful when you need to make a bold statement on the [...]-based overhead-projection markers work best on our vinyl mats as they are designed for plastic. DO NOT use grease pencils, permanent markers, or dry erase pens on the mats. The vinyl surface is too porous to allow for easy removal. It is recommended to first test any new pen on a small area such as the border, and wait at least 30 minutes before wiping off to insure that color wipes off properly. Often the colors that stain are not constant due to small changes in the manufacturing of the markers, so it is good to do this test whenever you get a new pen.