Thanks. I'm surprised you thought my comment was snotty. Yourself included, we have several people who frame their own work and those are the people I was referring to. I certainly wasn't looking for shoot-from-hip type answers.

I am NOT asking about a mount board. I am asking about backing board. In my case; however, they are often one and the same. For clarifications, I pointed to framedestination's website where it refer to the material (form core board) as backing board and named the material that I am using.

My question is that in this usage, I would imagine at certain frame size, thinner board (1/8") will be insufficient to provide enough flatness and stiffness and that use of 3/16" would be preferable. My question is, what is this size?

Would you be able to help me with that?

I apologize if you took offence to my choice of words but that was not at all what I was trying to say.