What is the softening temperature of styrofoam?
There are a number of different temperatures one could consider the softening point of atactic (randomly distributed phenyl groups) polystyrene, used in making expanded polystyrene :


Softening point: ~90 °C
Heat Deflection Temperature: 95 °C 
Typical Injection Molding Temperature: from 170 °C at back to 230 °C at nozzle