The Definition of UVC

• According to the World Health Organization (WHO), the three types of UV radiation are classified depending on their wavelength. They differ in the extent to which they can penetrate materials.
•  Short-wavelength UV is referred to as UVC and is the most harmful UV radiation. However, it is completely filtered by the atmosphere.
• The wavelength of UVC is 100 to 280 nm.

Material Transparency to UVC

• This Stanford University source reveals that short wave UV (UVC) cannot pass through most plastics or ordinary glass.
•  Most acrylic plastics do not allow UV-C wavelengths (100-280 nm) to penetrate.
• Also, very thin acrylic sheets of below 5 millimeters do not let UVC light penetrate.

Materials that are Transparent to UVC (100-280 nm)

• For really short wavelengths like UVC, suitable transparent media do not exist anymore, limiting the choices to reflective optics such as:
•  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.  
•  UV-grade fused silica is a material that is transparent for wavelengths that are down to 200 nm.
•  Cheaper standard-grade fused silica is transparent for wavelengths that are below 260nm.
•  Artificial diamond is transparent down to 230 nm.
•   Borate crystals like BBO and LBO also have relatively good UV transparency.

Summary of Early Findings

• Google Scholar did not provide any academic research that has been conducted on UVC transparency in materials or plastics. Also, any other research that seemed to contain relevant information was paywalled.
• We have provided the relevant information on the transparency of materials to UVC.
• The research did not reveal any plastics that are transparent to UVC.