They are white cotton (some are marked "Egyptian cotton", others just "cotton").
Size 15 1/2"
Style number 52
Note: I have several of these collars.
There are minor differences of detail in the packaging, and they have different patent numbers on, ranging from the late 1920s to the 1960s.
There is, however, no noticeable difference in the collars themselves.
You will need a pair of collar studs to attach the collar to your shirt.
These studs are available separately.