Switching from ribbed to foam spline

After reading some of your other posts about the foam spline being easier to install, I have decided to purchase foam spline instead of the ribbed spline that is currently in my screens. The current spline is the .150 ribbed. Would I need the same size in the foam spline, or do I need to size up or down when converting to the foam spline.
Additional info...I had previously purchased some .120 foam. It was super easy to install because it was smaller, but unfortunately it's not holding the screen in place.