Manufacturer page.

Zero thresholds are designed primarily to close the gap between the floor and the bottom of a door. This helps keep external elements like air, water, snow, and pests from entering the indoors. The threshold works in conjunction with other products such as weatherstripping and door bottoms to help protect the indoors. Zero thresholds feature top-quality materials and construction, designed to stand up to the demands of heavy traffic applications as well as those with extreme temperature differentials.