Pyramid Thing !!!

[LeedsRhinos]

Can anyone please shed some light on the following item we found on our neighbours farm here in NZ? It is a 500mm square thin card with 2 crossed pieces going up into a point, like a pyramid without the walls (if you will). So if you look down on it it looks like a cross on a square.
On the underneath of the square were the remains of a thick balloon and on the top was a glowstick. The whole thing was covered in silver foil and was very light.
TIA

[sddsddean]

Probably whats left of the radar reflector of a weather balloon. If you put 'weather balloon' into google and click on 'images' you will find loads of different styles. Heres a pyramid one.
http://www.abc.net.au/science/news/img/environ ment/balloon170106.jpg

[heathfield]

As the previous answer says, it'll be a radar reflector. The way they work is shown here.