Jenny @ Craft posted about these a while back – I think these plush particles would make great teaching tools.

WEIGHT: Particle weights vary according to their properties. The Higgs boson, top quark and W boson, for example, are the heaviest-they’re stuffed with polished gravel. The massless bosons are the lightest–they are stuffed with polyfill. The muon, a middleweight (very loosely speaking), is stuffed with poly beads. I tried to make the tachyon completely massless but I’m still waiting for him to return from the past (future?) to find out if it worked.