Originally Posted by Krio

In a bladder shock, shock oil cannot compress or expand, so for the piston to move up or down at all oil must flow through the piston. With an emulsion shock, there is air on either side of the piston that can compress and expend allowing the piston to move without any oil passing through the piston. This allows emulsion shocks to react more quickly to small/sharp impacts and is why many people prefer how they feel on 10th scale cars. However, bladder shocks are more consistent from the start of a run to the end and is why they are favored in 8th scale vehicles where consistency over an hour long main is key.