I am currently doing research on this one and am winding bobbins made of different materials to see how it affects the inductance or Q of the coil. I know plastics have different a dielectric constant and I am working on how it affects the sound of a pickup.

Below is the dielectric constant of various plastics used in making guitar bobbins.

ABS 2.4-2.5
Acrylic 2.2-3.2
Cellulose acetate 3.4-7.0
Nylon 6 4.0-4.9
Nylon 66 3.9-4.5
Polycarbonate 3.0
Polypropylene 2.0
PVC, plasticized 4-8
Phenolic 4.4-9.0
The above chart giving various dielectric values is information is from the William Bolton Engineering Materials hand book. I know there’s a relationship between the plastics and the tone of a pickup though it be subtle or extreme, there is a relationship between them.
There are other ways plastics are used in making pickups and guitar parts.

Bobbins can be injection molded or fabricated from sheet plastic and hand fabricated. The old Charlie Christian (Gibson ES-150) pickups were hand fabricated. The bobbins on the early P-90 pickups were also hand fabricated. The “Patent Applied For” humbuckers designed by Seth E. Lover were injection molded from 4 different molds. The Gibson Melody Maker, Johnny Smith and Firebird bobbins were injection molded out of nylon.

Still a good way of making bobbins is to stamp out flatwork from sheet plastics or phenolics and hand fabricate the bobbin to the desired shape. Many prototypes are hand fabricated this way and if the demand for a particular pickup is great enough then the manufacturer decides if they want to have an injection mold made. It cost much more for an injection mold but in a long run you have to decided if the labor for building the pickups will cost more than the cost of an injection mold. Injection molding can give you thousands of bobbins with equal tolerances and work well when machine winding multiple bobbins at a time. Hand fabricated bobbins work well with both automatic machine winding and hand or what I call scatter winding. Mounting rings used on the early Gibson humbuckers were also injection molded. The mounting rings for the Firebirds were stamped, polished and plated.

Early pickup covers on Gibson P-90s were vacuum or thermoformed. They take a thin sheet of plastic, heat it and shape it with use of a male cover form by pulling a vacuum. The cover is then trimmed of excess plastic. The pole piece holes can be drilled to the proper spacing by a drilling fixture.

Most all pickguards are made from sheet material with the earliest material called Cellulose Nitrate. This was very dangerous to use and would be difficult to put out if it caught fire when routing or machining. Many beautiful Jazzmaster, Jaguar and Stratocaster pickguards were made of Cellulose Nitrate and had to be changed due to the extreme hazard of this material. Early acoustic pickguards were made of thin sheets of this material.

I recently saw an old Telecaster where someone took a blow torch to the finish to remove it and got too close to the pickguard. I looked like a piece of peanut brittle when he got finished!!! Don’t do this!