The yarn chosen for plastic canvas is linked in part to the mesh of the canvas, which resembles a grid. Seven-count or seven-mesh plastic canvas is commonly available. The count refers to how many squares or holes the canvas has per inch for stitching.
Four-ply worsted weight yarn is a good option for seven-count canvas. The ply refers to the number of yarn strands twisted together to form a single strand of yarn, which enhances its strength. Worsted yarn fibres are typically combed before they're spun to straighten the fibres.
Five-count plastic canvas has fewer stitches per inch and larger stitching holes. Therefore, two strands of four-ply worsted weight yarn should be threaded through the needle and used together for stitching. Another option is to use a thicker yarn to allow for stitching with just one strand of yarn at a time. Suitable thicker yarns will have the word "bulky" or "chunky" on their labels.
Finer, more detailed stitching can be done on fourteen-count and ten-count plastic canvases because there are more stitches per inch. These canvases can accommodate yarns with less thickness. Look for a yarn labelled "sport-weight" for stitching on ten-mesh canvas. Pearl cotton is often used for embroidery and is suitable for stitching on fourteen-mesh plastic canvas.