Covering iR sensor Module

I am using an IR sensor module (https://www.amazon.com/HONG111-Infrared-Avoidance-Photoelectric-Reflection/dp/B06XKN15TT?ref_=fsclp_pl_dp_3) for my automatic dispenser system. Now, while mounting the IR sensor module in my enclosure, which material can I use to cover the IR sensor module which can allow the IR light to pass through below the glass for the hand to get detected.

I wonder what material is used to cover the IR sensor used in restroom flush systems.

They make IR transparent materials (plastic, glass, etc.)