CD-RW's are yet another step less reflective. They don't usually work in any CD players that were built before their invention (late '90s?).
If you are burning a CD-R that is only to be used in audio CD players, they often work more reliably if you use a slower burning speed. Even if the medium specifies 48x or whatnot, it seems the final quality is better at lower burn speed.
My trusty old Sony CDP-30 from 1985 - bought it new, never repaired, never cleaned! - plays most CD-R's, but not all (Canon as a notable non-worker), so the type of the medium has some effect as well.