I actually usually suggest flat white paint because of the longevity of it. When I contacted the company to find out how to clean mylar, they told me it couldn't be cleaned without losing it's coating so it's best to replace it. Flat white paint is 90% reflective, mylar 98% if clean, if you're really looking for every lumen find titanium white paint which is 95%.
I always suggest using some sort of reflective material as a lot of light is lost otherwise, just make sure there's still air circulation. Like Millworkman I like the insulated sheets with reflective material, cheap easy to hang and move out of the way.
I always suggest using some sort of reflective material as a lot of light is lost otherwise, just make sure there's still air circulation. Like Millworkman I like the insulated sheets with reflective material, cheap easy to hang and move out of the way.