It's agribon. Very light weight.
Agribon AG-19 Floating Row Crop Cover / Frost Blanket / Garden Fabric Plant Cover https://www.amazon.com/dp/B00LB3SC0A/ref=cm_sw_r_cp_api_X2QXzbKGVM15J
I learned from the spring season, broccoli likes some shade from direct sun, otherwise the leaves scotch.
We might have to give this a try!