It's made of Vinyl, like an LP! Or maybe a mixture of vinyl and conventional materials and hard fillers.

In the 30s UK Columbia produced just one record on vinyl. It was hard enough for steel needles, but some people used fibre and bamboo needles and these tore the records to pieces, so it was never used again until LP days.

These records noted "Khlorvinilovaya" generally do not differ from conventional records, and are not flexible. 1940-1941 in USSR saw a number of experiments with new materials, some of them close to Vynyl:
http://www.russian-records.com/details.php?image_id=8613
Aprelevka Plant also undertook some very curious experiments producing Soviet picture records, made of layers of shellac, paper and acethylcellulose.

Прекраснейшая по гармонии музыка и замечательное исполнение