I found what appears to be a similar product to Kodak Opaque.

http://www.bhphotovideo.com/c/produc...e_Masking.html
http://www.bhphotovideo.com/c/produc...e_Masking.html

Are Kodak films in 120 format such as Tmax and Tri-X polyester or "standard" base? (whatever "standard" might be??)