Door Skins

• A door skin is thin, 1/4-inch or so plywood used to make the outer skin of flat, interior, hollow-core doors. Painting panels can be made in much the same way the doors are made where frames are constructed first, then a panel, larger than the frame is glued to the face of the frame. The excess is then trimmed. (A router with a flush-trim bit works especially well.) Any thin, high quality plywood will work, but if it's a door skin, you know it's going to be smooth and free of surface imperfections.
  
  

Linen

• Linen is not the answer if you're looking for an inexpensive painting medium, as it's more expensive than artist's canvas -- but it's also a much finer weave. The texture of a weave is often desirable because it pics up paint from your brush. Some painters don't like a coarse texture, especially if they're painting a very realistic painting, which lends to linen.
  
  

Ceconite

• Ceconite is a brand of nylon weave. It is essentially a modern version of an airplane wing covering. Old bi-planes, for example, wouldn't have used Ceconite because it didn't exist, but they did use fabric over wood frames. Today's aviation fabrics are lighter, stronger, and fortunately they can be less expensive than artist's canvas and much finer than linen.
  
  

Masonite

• Masonite is another name for press-board or chip-board. This is different from 1/2-inch or 5/8-inch particle board. It's a very dense, 1/4-inch or so thick, press-board with one very smooth side and one side that has a texture similar to canvas. Typically artists use the smooth side, gessoing it -- often multiple times -- then sanding it smooth. The backside can be used, too if you prefer a rigid painting surface and want the texture. The rough side takes a lot more primer to get a decent texture. Consider white house primer instead of the relatively expensive gesso.