A quilt is a type of bed cover, traditionally composed of three layers of fiber: a woven cloth top, a layer of batting or wadding and a woven back, combined using the technique of quilting. A quilt is distinguishable from other types of blankets because it is pieced together with several pieces of cloth. “Quilting” refers to the technique of joining at least two fabric layers by stitches or ties. In most cases, two fabric layers surround a middle layer of batting (cotton, polyester, silk, wool or combinations of fibers) which is a lighter, insulating layer. Batting is often referred to as “wadding” in Britain. Some modern quilts are made with an upper fabric layer, quilted to a layer of microfleece, perhaps without a fabric backing. The most decorative fabric surface is called the “top”, and is the design focus. A single piece of fabric (a “wholecloth quilt”) may be used as the top, or the top may be “pieced” from smaller fabric pieces. Sewing together smaller pieces of fabric into a larger patchwork "block" of fabric creates the basic unit. The “patchwork” of the top is typically made of a series of blocks (all identical, or of diverse design), which are made sequentially and then assembled. The blocks may be separated by plain fabric strips, called “sashing”. The central design space may be small (a “medallion”) or dominate the top of the quilt. Many tops have decorative "borders", of plainer design, surrounding the central panel of the top and enlarging the quilt. The "binding" is the final edge of fabric that covers the entire edge, and seals the batting. Most modern quilts are made of 100% cotton fabric in a light weight. Early quilts were often made of "calico," which is a cotton fabric in a small, repeating print. “Muslin” is a similar fabric (the name derived from Mosul, where quality cotton fabrics were produced in the Middle Ages), of lower quality on average. Silk and lightweight wool are also used, but less commonly than in the past.