IMO, 16x16 is the minimum size for a hank you're likely to puff. Something to be folded, like a white cotton or linen can be smaller, but unless it's really thick fabric, I'd still want 16x16 to have the option of puffing. For some of my jackets, I could even use 18x18 to keep smoother silks from falling down in the pocket.
And, congratulations on the launch of your new line! The hanks in particular look great.