Heavy gauge aluminum. Fine enough to be an effective filter and to keep bees and bugs out yet strong enough to withstand damage from birds, squirrels, etc. Diameter: 0.010 (.28mm). Fine enough to be an effective filter, keep bees and bugs out Withstands damage from birds, squirrels, and more Diameter: 0.010 (.28mm) Durable, strong, long lasting screen Excellent outward visibility and curb appeal For windows, doors and porches Great air ventilation and insect protection Will not sag or rust