Can't tell you much about cellophane. When working with other polymers, we would decrease filler particle size (This usually increased tensile properties, but not always. You have to go back to instron testing to be sure). then the filler itself. If you have an RI(refractive index), or can look up the value, if the value of it of the filler and the polymer match, often they can be put together and "blend". So if the polymer is clear and the reinforcing filler is white, if the RI is the same, the cured blend will often appear clear. Many if, ands, or buts with this. It definitely takes a lot of playing around with to get everything to behave. But maybe, matching the RI of the reinforcng filler to the RI of clear cellophane would bean approach to try. You might be able to get a stronger, clear material.