I recommend you paint or spray with something that blocks mold and possibly insects, then hang (double sided tape or staples) mylar on walls. Paint floor flat white. Mylar is more reflective, and it reflects colors more true to source. If you use UVB mylar is the obvious choice since white doesn't reflect UV as UV, it's shifted to violet (black (uv) light effect on white.) Diamond vs Regular is more for the grower's ease of mind than the plants, bright spots move with the mylar fluttering in the wind, no negative effects...