I dont know about glare reduction as most coatings are a bright white, but aid in cooling. Elasomeric coatings remain flexible to temperature changes. Up here in the mojave desert, flat roofs are typically foamed with a elasomeric sealer over that in a bright white to keep the underside cool.

Here is a link that might be useful: kool seal

Light colors will reflect the visible spectrum of light energy but to reduce gain from the IR spectrum you need something with a low emissivity surface like polished aluminum or the films used between double pane glass.

I believe there are paints or coatings that are claimed to have low emissivity properties but I don't know to what degree they are effective or even if they are legitimate products. I find there are a lot of misconceptions and self-serving nonsense associated with infrared energy in building design so I recommend skepticism.

Aluminum paint (it contains powdered aluminum) has been used to decrease emissivity for a long time.

It's main weakness is that sunlight (and UV) tend to degrade the binder holding the aluminum down.

Back in '95, I rolled out some elasomeric on the roof of my shop # 1 to help in the longevity of the roofing, # 2 to keep the inside cooler in the summer. It has accomplished both quite well so far. Is it considerably cooler and by how many dgrees? I dont have scientific data for you, only to tell you that in my real world application. it worked for my shop/ roof.

Here is some information.

Here is a link that might be useful: chart

NREL is 'the place' where high tech products are studied
and given a quality rating.

A company now makes a quality product - see here:

http://www.reflectechsolar.com/

And if I'm mistaken due to short time what I want you to
find is a product either they or another company makes
which is a HQ reflective material that can take a pounding
for 10 years but is made not as a sheet but as a 1/2"
thick kind of woven material. You lay it on the surface
you want to protect and it reflects away heat and doesn't
get hot, itself, as its area allows air to remove any
absorbed heat.

I'm confused about the way you describe your situation.

If you block sun (1) before its inside then
you're done with the job. Any covering will do.

If it were me I'd put up cardboard for the summer and save up during Winter for my next Summer need of cardboard.

(1) sun is about 100 watts of heat / sq ft. or 1000 watts / st meter or yard (1 sq yard = 9 sq ft)

Please follow through on how you finish this and post
photos to a hosting site where we can have a look.

one site is simple and free at

http://www.bild.me/

Here is a link that might be useful: photo hosting - give us the last URL on the list