The energy produced in the core of the sun, moves out into the radiative zone as electromagnetic radiation. This zone is also packed with hydrogen and helium particles, and because of this, the photon has a tough time getting through this layer. All of the particles will either repel the photon or it will "eat" the photon and then "spit" it back out. This process will sometimes take hundreds of thousands of years before the photon reaches the convection zone.