Description The Twist Block project is a construction system based on hollow concrete blocks that was specially designed for use in slums. The hollow concrete blocks can be assembled and disassembled by hand as a modular, mortarless plug-in system. For the first time, any angles can also be realized, which is very decisive for the application in slums. With the PERI formwork, the hollow concrete blocks can be produced by the residents themselves in small local manufactories. This creates jobs and a construction industry directly on site. The added value remains with the people living in the slum. The first successful project was a concrete block factory in the Kibera slum in Nairobi (Kenya). A new school has already been built with the bricks produced there.