Could you show an example of your cylinder. I asume just setting the transparancy of the layer is not enough? It also depends on your background, maybe you want to add refraction as well? Some more info would be nice.
As you can see in the image, the cylinder has a label wrapped around it, but the white in the label should actually be transparant, so that you can see throught it, while the text and logo etc, still remain sharp and visible. The material should also have a plastic feel.
If anyone knows how to do it in photoshop, please tell me! :)