A farthingale is an ankle-length skirt stiffened with hoops of varying diameters at intervals up the skirt. it is underwear and thus is worn under the main dress. Basically, it is a big boned petticoat that makes people keep there distance from you.
Farthingales were a fashion of the late Elizabethan era (1570-1600) There were three main types:
The word derives from the Spanish "verdugado", meaning
"something distended by rods or hoops" - [Ewing]
Farthingales can be boned with anything - some recommend steel, some timber strapping, some reeds. It depends what you can find.
What is this? This is The Garbindex - a guide to making garb for recreationists (ie how to sew clothes that will make you look genuinely medieval, when 'playing' with such groups as the SCA, doing LARP - or even making something really genuine for drama.)
Use these resources to find resources that will help you create clothing that looks great - and real!