Although some filaments may theoretically be possible to use in the pen (if they meet the thickness and density qualifications) we strongly urge you to stick to the colors we currently offer. Our filaments are rigorously tested with our units to make sure they are 100% compatible and will keep your pen functioning well past its initial manufacturer warranty period. If you choose to use any other filaments from a third party supplier that is not approved by us, you effectively understand and accept that you are voiding any support or warranty offered by the manufacturer of the pen.