The past 40 years I have been an upholster. Mostly in the furniture line. I have done a few cars for friends and have always struggled with what to use for door panels and such. Panel board used to be what the pros used. It was a tar board made to repel moisture but it would eventually warp. I used to use wood paneling of the type used in bathrooms with a vinyl coating on one side. Putting the vinyl side toward the outside did help. I recently was introduced to ABS paneling. Im in aahh! Its advantages is unlimited. It comes in 4x8 sheets in different thicknesses. I use the 1/8 for door panels and have used thinner in a pickup headliner. The neat thing about it is it cuts very easy. Just scribe it with a box knife and it will break off with a clean edge. You can clean up the edges with a sanding block or I have used my 4 grinder with a sanding disc to adjust the edges or smooth them out. It can be glued with the ABS glue to make different patterns in the surface. For instance if you want a flamed pattern in the door panel or headliner. Just cut out your pattern, glue it into place and glue your material over the surface and form the material around the pattern. It can bend to odd curves and heated to hold its shape. The first photo is of the area around the side of the front window of my 40 Pickup. You can see that the last upholster used chrome screws to attach the windlace around the dash area. The second photo shows a panel I made to clean up that area. All it needs now is to be covered in material to match and screwed in under the widow molding. No screws showing and a very clean look. I made a pattern of the area, cut it out of ABS plastic and screwed it into the area using the stock molding holes. I used a heat gun to warm it up to the point that the ABS was pliable and used a screw driver to mold it into place. Take the heat away and in a few seconds it will cool and hold its shape. You can see the photo a before sample of this panel and the lower one is one formed to fit a 40-46 Ford pickup to go from the kick panel up to the door trim formed around the dash curves. <O</O In the headliner shot I made a pattern for the front forward edge. I transferred that to 1/16 ABS and cut it to width. You can slide it under the header and formed it down the back of the seat area and held in place with a couple metal screws that will be covered by the back panel. Heat doesnt work here because you cant heat a big enough area at one time to hold its shape. For the side headliner panel I transferred a pattern to 1/8 ABS to hold its shape better. The back corners were heated to hold its curve to match the corners. Now that I have it all in place, I can make patterns out of ABS to put any design I want in the headliner. Glue them into place and cover with material or vinyl. The easiest way I have found to make door panel patterns is to buy that cheap clear plastic at your local fabric store. Cut it a little larger than the door and spray with fast tac adhesive. Stick it to the door and you can mark the outside edges with a black felt pen. You can also mark any mounting points, armrest holes as well as door handle and window riser handles. Peal it off and transfer it over to you ABS panel and cut out your new door panel. All the hole should line up and you can cover with your choice of materials or designs. You can also see that I use automotive snaps to hold the panel to the door. I dont care for the spring clips that were used at the factory. Take your time and you can make it look professional and a substantially less in cost. The best place I have found to find ABS is to look in your Yellow Pages for any local plastics supply house. It runs about $40 a sheet depending on the thickness. One side is smooth and the other textured. I believe it comes in black and white but that doesnt matter if it is to be covered. You can use SEM vinyl spray in any color if you want it to be used in a restoration to look factory stock. As in old pickup kick panels or headliners. Good Luck!