Which ducting would I buy for 6 inch inline? Insulation question (I'm confused)

So I know with insulation the ducting is going to be larger than usual now this is confusing me.

I have a 6 Inch inline fan and I normally use 6 inch ducting. Do I buy 6inch insulated ducting that comes out to like 8-10inch or do I buy 4inch insulated ducting and that comes out to 6inch? Or do I buy 8in insulated ducting because the tube will be 6inch?

Im not sure if hte insulation is measured with the ducting width or not.

So I have a 6 inch inline do I buy these and they will work fine?

http://www.homedepot.com/p/Master-F...Silver-Jacket-F6IFD6X300/100396935?quantity=1

6" insulated ducting.

Also,if you can use oversized insulated ducting,it will allow for better/more unrestricted airflow which will cut down on the noise of air wooshing around in the ducting.

Good Morning Cannabis,I clicked on that link,does it take everyone to their hometown homedepot or are we close to each other?
I know we have a good many growers,so many I been thinking of opening a store

6". They measure the inside diameter, not the outside.