It's been around a long time, it has seemed expensive, but polycarbonate sheet still is just the best solution for machine covers and guards. You can see through it perfectly, it machines nicely, and importantly if parts fly off unexpectedly, they won't get through! It's tempting to try cheaper materials like pvc, but in my experience, you'll end up regretting it, because they just don't measure up. Visible quality matters, as well as technical performance.
