The most practical I think would be 1/4" luon board followed by a large ballon filled with jello, then another 1/4" peice of luon board. Wrap the entire mess with vinal/carpet layer to simulate hair/hide. Of course that would be a real pain in the but. I think 2 peices of 1/4 luon and the wet foam would be as practical as anything and still give you enough density to measure your results. I did some tests with differnt arrow weights and Rocky ti-100 and ti-85 grn broadheads last year. I was lucky enough to have several peices of foam isulation wraped in very light weight tin. This worked reall well and gave easy to measure results.