i came up with the idea, because every once in a while we just sleep in a side street in a city. since it's often illegal, we don't want people to know that we do that. so it's great if you can see out while nobody can see in...
how much do you pay for the info???

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but seriously:
the cloth is a silk used for lining. there are different kinds and i'm not the expert. i had my mum look into it, since it's her business

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the cloth is very light and slightly transparent. with the dark background inside the vehicle, it is impossible to look in.
i had velcro sewed to the curtains' corners. a self-adhesive velcro is glued to the hardtop where the curtains can be stuck on.
i love it - it really works.
hope that helps!
sven