If I were to create the illusion of a transparent wall (of glass for example) 1/4 thick in a box surrounding my character, does this wall grant me full cover?
This question is different from: Can an illusion give a player partial cover. That question creates a visible effect and asks about partial cover.
The core of the question is whether or not a transparent or translucent wall in and of itself, grants cover to those behind it. The above example is the best way I can think of to readily manufacture such a structure.
The reason I am bringing this up as the answer to this question may have impacts on another game mechanic, but is being asked in isolation for clarity.