How Much UV Does Glass Block? (Office, Car, Home)
A window-by-window breakdown of what glass really blocks.
Ordinary window glass blocks most UVB but transmits a large share of UVA, while laminated windshield glass blocks the bulk of UVA as well.
Since roughly 95% of the UV reaching Earth's surface is longer-wavelength UVA, the rays standard glass lets through are exactly the ones you most need to plan around indoors and in the car.
Questions we get a lot
Does UV come through windows and clouds?
Largely, yes. Standard glass blocks most UVB but lets UVA through, so windows at home, in the office, or a car's side windows still expose skin to aging rays (laminated windshields block most UVA). Clouds stop only a fraction of UV, so protect skin near windows and on overcast days.
Why does a car windshield block more UV than the side windows?
Windshields are made of laminated glass — two layers bonded with a plastic interlayer — which blocks most UVA as well as UVB. Side and rear windows are usually single-pane tempered glass that stops UVB but lets significant UVA through, which is why long-term sun damage often shows up more on the driver's-side face.
What is the difference between UVA and UVB rays?
UVB rays have shorter wavelengths and cause sunburn, affecting mainly the skin's surface; UVA rays penetrate deeper and drive premature aging, wrinkles and pigmentation. About 95% of the UV reaching the ground is UVA. Both damage DNA and contribute to skin cancer, which is why 'broad-spectrum' protection against both matters.
r/AsianBeauty: 'Why do K-beauty sunscreens talk about UVA so much more than US ones?'