High power projectile weapons, often firing their rounds near the speed of light, are a staple of sci-fi. Under certain assumption sets these weapons are valid, I'm not interested in the science (or lack of) around how to build such a weapon, but I have wondered for a while about one particular aspect of such a weapon, detection. This excellent answer indicates that any projectile travelling near the speed of light will be reduced to a cloud of plasma by its continuous impacts with the atoms and dust of the stellar medium very rapidly. At lower relativistic speeds you'll see the same effect just a bit slower. Even if we assume that the projectiles in question are travelling slow enough to make their designated trip they'll still shed some mass to, and be lit up by the energy from, molecular impacts during the trip to their target. The glowing plasma they'll be surrounded by will make them relatively easy to detect en route and possibly defend against in some way.
Is there some material that a relativistic projectile could be sheathed in that would minimise this effect and allow such weapons to go unnoticed in transit for as long as possible?
In answering this question ignore the larger impacts with dust and micro-meteors they're going to be both rare and due to their size unavoidably highly destructive. Concentrate on the effects of the solar wind and it's mitigation, and projectile speeds of approximately 10% light speed.