TDK’s magnetic tape formulation had achieved relatively high recognition, with their formulation named Super Avilyn (sometimes abbreviated to SA) used in high quality audio cassettes as well as video cassettes. This spanned a very long time, and it seems their HR and HS series cassettes may have been based around this type of formulation. None of the cassettes are still in my possession, but here is an early cover which dates to 1980.
The cover seems to have yellowed somewhat and is plastered with labels (unfortunately) of the TDK HS series, which came much later. The cardboard is substantially thick, as expected for something of quality, Made in Japan.
The cover below is for a later cassette, HR series, but with much thinner card, still Made in Japan.