The U-90 set is a component based set that can expand in weight to meet the needs of the user. This set has a urethane coating and adds more comfort to the wrist. You can start with the U-90 Stage I, 5-50 lb set. This set can then be expanded later to 70 lbs or 90 lbs per hand using the Stage II - 70 or Stage II - 90 Kit. The U-90 set can then be further expanded with the Stage III Kit to 125 lbs per hand.
The U-90 set (or any PowerBlock for that matter) is the most compact dumbbell available. The small size of the PowerBlock keeps the weight concentrated closer to your hand making the dumbbell easier to control and balance. The U-90 set also comes with two 2.5lb weights to allow the user to make smaller incremental changes.