Vellum
Here's my trick for natural looking Vellum.
I
never use the pure white, as they tend to be to static looking
(but it does the job!)
Apply a gradient on your desired vellum.
Light gray - white - Light gray - white - Light gray
(For this example, I have made the gray darker than the one I
usually choose)
Change
the layer opacity between 10 and 50%.
If you want your text to also "reflect" the light, just
put the text layer underneath the Vellum.
Add
a bevel and a shadow to your vellum, but keep it soft.
You can also add a "satin" layer style and experiment
with textures for an even better result.