Depends on how much bracing you have, I used 1/2 inch and it was plenty for my flooring and it is lighter too, but if you are spanning a large gap you might want to go 5/8. Lay a piece down and walk on it. If it flexes more than you like go thicker or add another aluminum brace, Me, I like light weight so 1/2 inch and aluminum bracing is my choice.