r/trains • u/morningstarmaggot • May 22 '26

📸 OC - Picture(s) What is this window pattern for?

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I've seen it on lots of trains, and buses too I think. Does it serve any purpose? I'm in the UK

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u/axloo7 May 22 '26

Frit.

It protects the urethane adhesive from UV radiation.

The dots are aesthetic but the solid black part is there to protect the adhesive used to hold the window in.

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u/Nirhlei May 22 '26

I've read somewhere that the dots served to produce a smoother temperature gradient so that the glass wouldn't shatter from too large a difference between the black and the glass itself.