Flat white paint will do just as fine IME, but use a quality paint that is washable.
It will be easyer to clean your room, also panda film, mylar or what ever will get stained really fast.
And you will in no time loose the extra reflection, unless your only using RO water for folia sprays.
I folia feed with fish mix once a week, using pH adjusted tap water and that leaves a lot of stains.
The only reason I use Alu reflective material, is for the IR reflection/insulation and nothing else.
Panda film is awesome at blocking light, so for that reason I have in the past used miles of it. Easy to split up rooms, for very little money, with a stud wall and panda film. Very hard to clean tho, without ripping the film, where its stapled to the studs.