Japanese Pressing Vinyl question

Ever hold a record to a light source and tried looking through it? I'm sure you're well aware that you can see through the MFSL pressings, not the heavier ones silly. I proceeded to examine other japanese pressings, ie non-MFSL half-speed and regular japanese pressings, and to my surprise they were the same type of vinyl!

Is this a special type of high purity virgin vinyl and something worth looking out for? Is this type of vinyl purely manufactured in Japan?

curious george ;^)