Full Idea
The quarks provide very little of the total mass of a proton, and the fields created by the virtual particles contribute most of the energy that goes into the proton's rest energy and, hence, its mass.
Gist of Idea
Most of the mass of a proton is the energy in virtual particles (rather than the quarks)
Source
Lawrence M. Krauss (A Universe from Nothing [2012], 04)
Book Reference
Krauss,Lawrence M.: 'A Universe from Nothing' [Simon and Schuster 2012], p.70
A Reaction
He gives an artist's impression of the interior of a proton, which looks like a ship's engine room.