This finger lock design is already used for ages in for example wooden furniture, to create strong corner connections. Therefore Policart choose this design to connect there blankets on the rotaly cylinder.
The Polyurethane blankets are joint into the mould with fibreglass backing, to create a tight fit around the cylinder. An other advantage of this fibreglass backing is the already curved shape, which means that the blanket is easier to mount, caused by the forgiven strength of its shape.