Most acrylic plastics will allow light of wavelength greater than 375 nm to pass through the material, but they will not allow UV-C wavelengths (100–290 nm) to pass through. Even very thin acrylic sheets of less than 5 millimeters (mm) do not let UV-C light penetrate.

What material can block UVC?

Highly purified calcium fluoride(CaF2) is a material that is UVC transparent since it can be used down to 160nm. This is the same case for other fluorides like Magnesium Fluoride (MgF2) and Lithium Fluoride (LiF). Lithium Fluoride is UV transparent down to 110 nm.

Is acrylic sheet UV resistant?

Acrylic is inherently UV resistant with as little as 3% degradation outdoors over a 10-year period.