You made test peps out of the foam and it was too big? As for making a helmet out of foam, I can't really help with that since I don't think a helmet looks too good being made from foam. I don't think the foam will be able to hold up to the visor if the visor needs to be forced in the helmet and the visor may just pusg out the sides of the helmet and cause the helmet to look funny. XDAwesome, thanks HG.
The part about adding an inch to my measurements for foam really confused me, mainly because I'm a fairly small person (5'3". D, and when I made a few test peps for the arms and helmet (just to see if it actually fits, practice, etc.) I found that they are really too long/wide/tall (if not all, then either or) for me because I added that extra inch. Just for clarification, the extra inch is only for measuring the torso or for all body parts?
Great to know this information, HG. =D I just haven't found an actual file that said "Kat's Knee Pieces" on the Halo Reach pep database, so I actually had to look through the Halo Wiki to find which pieces closely resembled Kat's armor and picked it. The information regarding how to scale it was very helpful! Thanks!
As for adding the extra inch or 2, I did it for ALL of my pieces except for the handplates and boots. Handplates don't really need the extra inch to them and I scratch built my boots. And adding that extra inch ONLY applies to when working with foam. When it comes to the helmet, some people will add 2 extra inches to leave room for padding and any fans if they plan on installing them since they will also need the room for the electrical work.
Also, for Kat's knee piece, go to the Reach pep thread: http://www.405th.com/showthread.php/24086-*The-Official*-Halo-Reach-Pepakura-Files-Thread and go to the bottom of the 2nd post. The file was made by Rhinoc and above the picture lists all the links.