[Maurin] used several lengths of conductive fabric, a perforated foam core, and an Arduino.

Pictured above is the foam core being punched. The holes will create contact points between the conductive layers. The grid shows where the keys of the keyboard will be in the finished version.

After that, the conductive layers, and inner foam layer are sewn together. The conductive layers are placed in opposing directions, creating a switch matrix.

An Arduino is used to translate each step into a button press. While full design specs are nowhere to be found, the higher resolution photos on [Maurin]‘s Flickr stream should give you enough of an idea to build your own.

[via ladyada]