I had a bit of a struggle with some FT Builds - keeping the weight down!
Did a check: I found on the FT forum the following information
Weight of
$ Tree Foamboard : 0.19 gram/square inchWeight of
Australian foamboard: 0.39 gram/square inchWeighed mine (
Foamboard, both sides paper laminated) 390 grams, 23.5"X 35"", thickness 6 mm
or
0.49 gram/square inch.Ouch!!
Weight of 5 mm unlaminated board (
biofoam) 132 grams, or
0.16 gram/square inch