The Petticoat
The petticoat was another name for skirts during the 18th century and was worn by females of all social classes.  Later in history petticoats came to be known as a slip or a layer of underclothing.  The 18th century woman usually wore at least two and sometimes more petticoats at one time, for modesty and warmth, and in general most were interchangeable.  There are, however, surviving examples of petticoats that clearly are meant to be used as the innermost layer, or underpetticoat.

Petticoats were usually made out of linen, silk or wool, depending on the wearer's class.  Silk petticoats were usually made to match a gown of the same material and ruffles or ruching of the same fabric was sometimes used along the hems. The more common woman wore plain petticoats and they were often solid of color, although sometimes found vertically striped, 

Petticoats usually had a gathered or pleated waistband, either on self fabric or again on woven linen tapes. Many petticoats that are extant have lost their original waistbands due to wear or upgrading or retrofitting during the 19th century, a fate of many original garments.  The hems were often bound with woolen or linen tape to prevent wear at the hems.

The petticoat had a slit on either side at the top to allow the wearer to reach into the skirt and access her pockets, which were a separate garment altogether for the 18th century female, although pockets were integrated in men's garments.