OK

[RaspMetalicMX3SE]

I'm gonna buy a Kicker sqaure very soon and i wanted to know what the best material is to build a box out of?

[Mean_Machine]

3/4" k4 (i dont remember exactly what its called something like that). if you cant find any of that use the most dense plywood you can find like pine or something for building cabinets with. those solo-barics hit hard and if you have bad wood its gonna sound crappy. hopefully that will be of some help

[92RedMX3]

You are looking for 3/4" MDF. That is what is used in professional installations. Well that and fiberglass commenly.