Palco and Accuform (two companies, same process), use a process called Thermoforming or Vaccuum Forming.
They start with a sheet of pre-grained ABS plastic and heat it up, then it's dropped down over a mold shaped like a door panel. Vaccuum sucks the softened sheet down over the mold and you end up with a sheet shaped like a door panel with a flange of excess material all around the base of the mold. The excess flange is then trimmed away (usually by hand) and then any factory designed under cut areas required to attach the panel to the car (which are not possible to add during the thermoforming process) are glued or rivoted to the main panel.
Originals were made from injection molded thermoplastic polypropylene (hot molton plastic) which is squirted under tons of pressure into an enclosed steel mold to form the door panels entire shape, inside and out including the distinctive grain.
As noted originals were injection molded in Polypropylene, not ABS, these two materials have hugely different properties, Polypropylene is VERY resistant to most solvent based chemicals (which is why it's hard to paint) while ABS is EASILY attacked by most solvent based chemicals, so, with a reproduction if you get gas, thinner, or some other solvent on your fingers, touch the panel = Gooey fingers and a messed up panel, not so with originals. ABS is also a stiffer material and will not deaden road noise anything like original Polypropylene panels will (PP is a softer pliable material that absorbs more sound).
JD panels use originals which gives you the factory mounting points, sound deadening properties, and chemical resistant properties. They also use a thermoforming technique to restore panels but rather than forming a rigid sheet of ABS plastc over a mold they wrap the original panels with a flexible pre-grained vinyl skin (vinyl/PVC resists solvent based chemicals much better than ABS) and rather than a mold, your door panel is the mold, the panel is cleaned, sanded, glue is layed down, and the skin goes one. The negatives to this process are that the door panels do become slightly larger because of the new thin vinyl skin which can lead to some tight fits where panels meet, (most cases I've seen have been minor though), the vinyl grain is slightly different than original injection molded panels, and due to the fact that you will need to get ALL of your interior panels recovered so that the grains and colors will all match, the cost can be pretty high (however, thislast comment applies to Palco and Accuform as well).
Bottom line? It's a personal choice, nothing will beat nice originals, period. IMO JD is the second best way to go, after that it's a brand decision on Thermoformed reproductions.
