Best cheap plastic for DIY whiteboard

I have gone through many different versions of whiteboards; purchased and DIY. Quickly, they all become terrible and the ink is difficult to erase. I tried car wax to condition the plastic as well with little results. I ended up stumbling upon a fantastic solution: I cam across some pieces of glass with rounded edges that were used for a shelving project. There were about 2'x3' each. Mounting these on the walls in our office was easy using some stylish brushed nickel mirror hangers. They work amazing and I highly recommend seeking out glass as an alternative.