We evolved models of giant planets based on the disk instability mechanism. We used a stellar evolution code (Kovetz et al. 2009) that was adapted to handle planetary evolution, and a code for estimation of opacity for gas and grains mixture. The models we ran were for one Jupiter mass bodies, composed of solar mix of hydrogen and Helium. The initial radius of the protoplanet is approximated equal to its Hill sphere radius. Typically, it contracts slowly for a period of several 1e5 years and then undergoes a rapid collapse to planetary dimensions. We find that these parameters have significant effects on the evolutionary behavior. Changes in the opacity parameters (grain size distribution and grain amount) can change the time of onset of rapid collapse by a factor of two or more. In addition, under some conditions, the protoplanet oscillates about some pre-collapse value of the radius for extended periods exceeding several million years. Peak luminosities just before collapse can exceed 1e-5 solar luminosities.