The four stamps that make up this set of stamps together make up a design that is repeated over the total pane of stamps. Thus, the pane itself takes on the appearance of a small quilt. Quilting is a needlework technique used to hold a layer of insulating or padding material between two outer layers of fabric. To prevent the interior layer from shifting, numerous runs of stitches lie across the sandwiched layers. Several types of quilting are known. Wadded quilting is evenly filled with thick padding. Flat quilting has little or no padding. Trapunto has parts of the design raised by being heavily padded. Corded quilting, also known as Italian, features heavy yarn threaded between double rows of stitching. Patchwork quilts were an extremely popular form of folk art in preindustrial America.