No fabric that I know of has a different transparency on either side.
When you're looking to have something you can see out of but can't be seen back through, you're looking to take advantage of what is sometimes called "the scrim effect." When you view scrim in even lighting it is highly transparent, but when you exaggerate the lighting differential on each side, the fabric from the brighter side appears opaque, and when viewed from the darker side it appears transparent.
Try it out. It's the same reason why your windows become mirrors at night but are completely clear during the day.
-Nick