Which fabric blocks the most heat?

For cutting heat and glare while keeping airflow and a view out, Suntex 97 is the strongest choice. It blocks about 97% of UV rays.

SolaMesh shades from above while letting air through, with darker colors giving the most shade.

Sunbrella blocks the most light because it is solid, but it holds more heat because less air passes through. Heat retention is usually not an issue unless your space is fully enclosed.