The decisive factor is primarily the type of window
Windows with single glazing can be retrofitted with window film from the outside and inside without any problems. Other types of glass, such as double or triple glazing, safety glass, sloped windows or thermal insulation glass should not be covered with solar control film from the inside. The sun's rays reflected and absorbed by the film cannot escape. Heat builds up and can sometimes even cause glass breakage.

Hello, according to a specialist, the film should be laid on the outside, because the glass won't be able to withstand the heat if the film is laid on the inside.

Good day
I don't know, I haven't fitted them yet.