MDF is still the most popular product we supply for backing picture frames, although many alternatives are now available. MDF is inexpensive, it's relatively light and stable, and cuts easily with a knife or on a wall mounted cutter. Cutting MDF with a saw is not recommended as very fine dust is produced which should not be inhaled.
We only list the popular 1220 x 915mm (48" x 36") boards here, but we also stock 2440 x 1220mm (96" x 48") boards in 2mm and 3.2mm thickness. The larger boards are difficult to send by carrier - ask us about our van delivery service.