advantech over advantech?
 

I am in the process of building up my bathroom from the joists up, I have one layer of 3/4" advantech down now. I am planning on adding another layer of 1/2" plywood over the advantech.

Is there a better material to use other than plywood, should I use a second layer of advantech? Any advise would be appreciated, thanks.

If your tileing, 1/2" concrete backer board?

The Advantech doesn't seem that much stiffer than plywood.
http://www.advantechperforms.com/advantech-advantage/strength-stiffness.aspx
Don't forget to stagger the seams of the sheets.

http://www.advantechperforms.com/uploads/resources/installation/AdvanTech%20Ceramic%20Tile%20at%2024%20oc-06082010123729.pdf

http://www.schluter.com/print/media/datasheets/schlueter_db_uncoupling_us_0806.pdf

this is going to be for a future hardwood floor. I guess I can get away with 3/4" subfloor if I go with 3/4" wood. I need to make my mind up

I'm not a fan of hardwood in a bathroom. You should be able to put the hard wood on that floor. If you do put down another 1/2", make sure you glue and screw it well and longer screws thru into the joists and as suggested offset joints.
I just can't imagine how you would protect the wood from getting wet sooner or later.
It on takes one time.

I mixed posts here, I was planning on putting wood in the living room which also needs an under lament. I never planned on putting wood in the bathroom, that was my mistake.

Good, I have seen bathrooms with hard wood, don`t like it.