What do you call that glass that turns white?

Its a kind of glass used in some prominent offices in the US, like in the pentagon sometimes.....I saw it used in the movie True Lies, when Arnold Swarzenneger and his friend were in a tunnel and where an x-ray was carried on them why they were in the tunnel and then at the end of this tunnel was this glass door that was completely made of white glas then when a woman pressed a button the door became trasparent...

I believe you are referring to 'Smart' Glass.

Here's an article: http://en.wikipedia.org/wiki/Smart_glass

Hope This Helps.

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