Reflectix, the shiny, aluminized bubble wrap can be good for some
insulation applications. Used often in window shades in hot climates.
I've heard of folks adding it into their cabin-tops when replacing
headliners. If carefully glued and taped, it's also a vapor-barrier.
It is actually aluminum-coated, leaving black marks on things it rubs
against, and might be of some concern for galvanic interaction with
other metals.

Aaron
www.navagear.com - the gear and gadgets blog for cruisers
s/v Sweet Destiny