The records on the cereal boxes and most importantly inside MAD Magazines ("She Got a Nose Job" and "It's a Gas" were 2 childhood favorites may find them on YouTube) are thin flexible vinyl (PVC). They are made by Eva-Tone Corp. in Illinois and now also FL. I was at the factory in the 70's. Had them stamp clear Fresnel lenses (similar to record grooves- we furnished the stamping masters) in continuous rolls then cut into squares on same production line as the records. We used them in our Psychedelic/Disco color organ sound to light boxes, made for folks like Spencer Gifts, Radio Shack, etc. Stayin' Alive in the good old days.
is the sound of vinyl due to the physical process of the turntable?
Same here. I do not own a turntable, however, if the sound of vinyl comes from the physical act of the record on the turntable why can't I transfer digital audio or at least emulate that process to digitally recreate that sound? I remember back in the 1970's you had 45rpm records on the back of cereal boxes and they were not vinyl, however they sounded good why can't I do that myself?