These Chaco Pens come filled with a white chalk. You can of course use the white chalk that is in it but we offer it here as a way to match our Blue, Barely Blue and Pink chalk that's in our Pounce Pads. You can use up or dump out the white that is originally in the pen and fill it with some of the extra chalk you have from your Pounce Pad. This way touching up stencils is super easy. You can also the pen for other lines and marks you may need when working with precuts or building blocks in general. There is a nice beveled edge to get close to the ruler edge for a great mark. Refill them as you need to.