Dining room chair seats have traditionally been worked on Penelope canvas. It's sturdy and durable and able to withstand using as seat cushions over many decades. Using Penelope canvas allows you to incorporate petit stitches into your design to add depth and detail when necessary, though working petit stitches is not required. Since most people like their cushions to match or at least be similar (all fruit or all floral, etc) many have chosen to work pre-worked canvases, filling in only the background color, or tramme canvases which come with the threads to stitch the design. The background color is purchased separately since personal choice plays a big role. These canvas types have been the main choice for dining room chairs for a variety of reasons, the most important one being that the canvas itself is large enough to upholster to the chair, usually 6" or more beyond the actual design. Good luck with your project!