1" neoprene bonded washers seal the screw holes when you fasten polycarbonate panels to framing. The bonded neoprene compresses against the panel as the screw drives home, keeping the hole watertight while the panel is still free to expand and contract. Each bag holds 100.

Use them with #12 x 1.5" self-tapping screws, one washer per screw, to secure the sheet to your structure. Drill the panel holes slightly oversized so the sheet can move, then drive each screw just until the washer seats flat against the panel and stop there. Going further dimples the sheet and can cause leaks. It's a small part, but skipping it or overtightening is a common cause of leaks at the fasteners.