I use ultra flat black paint on a rough surface, probably, my opinion is that felt is best of all, but challenging to apply. The main thing about baffling is to make sure that no undesired light ray can make it to the focal plane. Often, upper ends are not long enough to cut off light streaming past the diagonal into the focuser.
My tubes are truss assemblies. I use a single upper ring that holds the focuser, spider and truss attachment assemblies. I put a baffle ring just under the focuser and a baffle about the size of the primary opposite the focuser. Many traditional upper ends do not extend far enough up and down to prevent light streaming past the diagonal from entering the focal plane. Also, the mirror end needs to be baffled. The test is to grab a powerful flashlight, have someone looking through a low power eyepiece, and ask them to tell you when the view through the eyepiece changes. You move the flashlight this way and that, seeking chinks in the baffling armor by trying to get some light into the focal plane.
You are only a true ATM if you go to the beach and sort your own grit, make your own glass in a kiln, and grow your own trees to make plywood from.
Mel Bartels