A'a get's more cooling because it shoots up in the air and then get's goopy. It has high viscosity. It has the same chemistry as pahoehoe. This is a picture of Pahoehoe lava. It is rocks and fragments of lava that eject from a vent.
Pahoehoe is smooth lava.
When the erruption is going out it comes out sliding over the top of the top of the volcano and makes it's way quickly down the hill and through the lava tubes.