why does nasa use that interesting reflective material in space vehicle constuction?

Answer 1

Those materials helps to reflect unwanted cosmic energy away from the shuttles.

i.e: it prevents harmful lights like Cosmic rays and UV rays etc getting in to the shuttle and damaging Human (if any) and mechanicle parts.

It also helps reflecting the heat / radiation (from sun and generated from the friction from getting in and out of the earth's atomosphier) hence protecting what ever inside.

The matirial also helped to maintain the internal conditions (mainly the temprature) of the shuttle in the normal range.

This is a very good methodology since those meterials were very light (unlike other heat & radiation resistant hevey materials)

the smooth surface also reduses the friction and hence helps to gain high throtal in less time and spending less energy (fuel)

Answer 2

You mean like the gold foil they used in the pre-shuttle days? That was used to keep the crafts and components from getting too hot from the heat of the sun.