Is glass/clear plastic see-through when astrally perceiving?

The basic rule of thumb is this: if you can see through it in the physical world, then you can see through it on the astral plane. If you can't see through it physically, then you can't see through it astrally, either. The only real exceptions are astral barriers (and other astral things), which are at least partially opaque on the astral, but physically invisible.