This is good for the hat blockers health and the general environment.
To block a hat, we first dampen the felt body on a steam table.
Once the felt is nice and moist, it becomes more pliable. It is then placed over an aluminum mold (hat shape). The flange is roped (tied) onto the mold and the felt is stamped between the top and bottom mold. The molds use to be heated using coal generated flames. The hot molds press and dry the felt into whatever hat shape they represent.
He then presses the bottom mold into the top mold.
The molds are intensely hot. The felt sits between the molds for a few seconds during which it is pressed/ironed into shape.