Cauls were worn by themselves during the latter half of the 16th century, as well as being worn under flat caps, tall hats, toques, veils, bongraces, and a wide variety of other headwear. A woman's hair was pulled back into a bun or coil and a caul fixed over it.
Cauls could be of simple linen, or of ornate gold and silk work. Networked caules were common. This caul has a base of white linen, laid over with purple cloth of gold (warp of purple silk, weft of metallic gold thread.) A design in purple velvet is appliqued on top. The outer design is edged in silver cord, couched around the edges, and the inner design is edged with a border of glass pearls. the applique is accented throughout with tiny beads of clear crystal. The inspiration for the design came from the decorations seen on the stomachers and gowns of women in Lucas Cranach's portraits, and by some pictures of velvet cloaks in Arnold's Patterns of Fashion.
You'll find more information on Elizabethan Cauls and their construction on this page about Elizabethan Cauls and Snoods.