I used this "TekFoil" product on the walls and ceiling of my garage, I don't see why it wouldn't work in your barn.
http://www.teksupply.com/farm/suppli...nsulation.html
Staples up quick & easy, is virtually fireproof (I tried on a sample
) and keeps the heat in (in the winter) and the sun's heat out (in the summer).
The interior of the garage is way brighter, the lighting is much more effective.
I liked it so much, I used it behind the sheetrock on an addition to my house.
A similar product is available at Home Depot.
http://www.homedepot.com/webapp/wcs/...1&distance_1=5