The LilyPad Arduino is a set of sewable electronic components that allows you to build your own soft, interactive fashion designed circuits for wearables and e-textiles. It opens up a whole new world of possibilities when creating the most fascinating microcontroller projects. Oh, and it's washable!
LilyPad Arduino - A Sewable Microcontroller for Designer Circuits

LilyPad is a wearable e-textile technology. Each LilyPad was creatively designed to have large connecting pads to allow them to be sewn into clothing. The LilyPad Arduino can be sewn to fabric and similarly mounted power supplies, sensors and actuators with conductive thread. Various input, output, power, and sensor boards are available.
The main board consisting of an ATmega168V (the low-power version of the ATmega168) or the ATmega328V (the low-power version of the ATmega328)with the Arduino bootloader and a minimum number of external components to keep it as small (and as simple) as possible. The Lilypad Arduino board will run from 2V to 5V.
The back side of the LilyPad is completely flat! It uses a surface mount programming connector to keep the header from poking through.
The LilyPad Arduino is washable! (We recommend washing projects by hand with a mild detergent. Drip dry.)
Footprint:
The LilyPad Arduino is a circle, approximately 50mm (2") in diameter. The board itself is .8mm (1/32") thick (approximately 3mm (1/8") where electronics are attached).
A breakout board for FTDI USB is necessary to program the Lilypad.
