From Introversion Software:
This month we've returned to our boffin-like roots and implemented a thermodynamic model. When the sun sets over the outer fence and the shadow of the sniper grows longer over the exercise yard, the temperature will begin to drop. Heat sources like the kitchen and radiators will keep things warm for a while, but the cold will start creeping through those thin cell walls.
Next comes Quick Build. Stolen straight from the console build comes the ability to stamp down whole cells and offices, This should make things a whole lot quicker and a bit less "grindy".
We've also packaged up some of the coolest prisons we could find so if you don't use steam, or your connection drops you still have something to play with. Along the same lines you can now filter the most popular steam prisons in game and tinker with the most popular penetentiaries on the workshop.
Get Update 4 here.