Hi there, I recommend a large size. My large sized bionic back protector is a perfect for for my A* textile scout dry star jacket.

Large

A large size is recommended.

The small is 14" tall and 10" wide at the top and 7" wide at the bottom.

Without the foam, the back protector fits in nicely in my sand jacket however if i tried to put both in it will distort the back of the jacket.

I just put mine in outside the foam i.e. foam closer to my back, for a bit of added comfort and protection. It still fits snugly, and bulks the jacket out a bit too. I doubt leaving the foam in or out will make much difference if you prang

I guess it really depends on the type of jacket you've got and how thick the foam piece is and how much room you've got. I tried doing just that with my Shift jacket and both of them just wouldn't fit inside the sleeve for the armor.

Thanks for the replies everybody.

However...
Upon inserting this back protector into my Tech 1-R jacket, I realized that it flops around unless the factory foam piece is in there with it. It adds a little more bulk, but it is totally manageable. It just doesn't feel right on its own.

Thanks.

I guess if the foam piece AND the SAS Tec piece both fit in your slot in your jacket it's probably not a horrible idea to use both. I would think this would get really uncomfortable and would restrict air flow. The sas tec armor manufactured and tested to withstand the hardest impacts by itself, so it's not necessary to use both. Also, the sas tec piece is much more flexible and body conforming then the foam, so the foam might restrict you from getting the full perks of having this armor.