The Kettle Blocks are like the PowerBlocks compact, space-saving, portable, cost effective and easy to use. They are, like the Flex Series, made of steel and urethane, and the weight is easy to change with the flexible pen. The Kettle Block 20 lbs is equivalent to 5 kettlebells, with a total weight of 27.7 kg (61 lbs). The maximum weight of 20 lbs Kettle Block is 9.1 kg. The Kettle Block 40 lbs is equivalent to 8 kettlebells, with a total weight of 84.4 kg (186 lbs). The maximum weight of 40 lbs Kettle Block is 18.1 kg.