  We study thermalization of the early Universe when the inflaton can decay
into the Standard Model (SM) quarks and gluons, using QCD arguments. We
describe the possible formation of the thermal plasma of soft gluons and quarks
well before the completion of reheating. Relevant interaction rates of leading
order processes and the corresponding thermalization time scale is presented.
We discuss hadronization while thermalizing the decay products of the inflaton,
when the reheat temperature of the Universe is below the QCD phase transition
but above the temperature of the Big Bang nucleosynthesis.
