This thing is -270°C and is EVERYWHERE

P₁ V₁ . . P₂ V₂
-------- = ----------
    T₁ . . . . .T₂
Your dry shampoo can got colder because of the equation, shown above. Both V₁  and  V₂ are the same value (note that 'V' stands for volume.) However, P₂ is necessarily smaller in magnitude than P₁ (note that 'P' stands for pressure), so, in order to maintain the equality expressed by the equation, T₂ has to compensate by being *smaller* (in magnitude) than T₁ .  Since 'T' stands for temperature, this means that the final temperature inside the can (i.e. T₂) is _colder than_ the initial temperature inside the can, T₁ .