What was the first vinyl record ever pressed?
According to The Record Collectors Guild:
In 1930, RCA Victor launched the first commercially-available vinyl long-playing record, marketed as "Program Transcription" discs. These revolutionary discs were designed for playback at 33⅓ rpm and pressed on a 12" diameter flexible plastic disc. In Roland Gelatt's book The Fabulous Phonograph, the author notes that RCA Victor's early introduction of a long-play disc was a commercial failure for several reasons including the lack of affordable, reliable consumer playback equipment and consumer wariness during the Great Depression.
The article also links to this webpage, which explains:
Thus, the 1930 RCA Victor Catalogue introduced their LP record, the 'Program Transcription.' This new kind of record was RCA's hope for restoring their market. By 1930, radio and the depression had reduced RCA's and all record companies' sales. The 'Program Transcription' was 12" in diameter, revolved at 33-1/3 RPM, had fine grooves (.0045 inch) that were closely spaced, and was made of a flexible plastic called 'Victrolac.' It carried up to 'three times' the playing time of a 12" 78, had quiet surfaces, and was to be played with a 1.5 mil RCA Chromium Orange Needle.
If you search for Victrolac, which seems to be somewhat synonymous of vinyl, you'll encounter things like this.