Do you mean like double layer? Several of us have made one that is really simple. You use a provisional CO, knit the hat and finish it off. Then pick up the CO stitches from the provisional CO and make another hat the same as the first and finish it off. When it's done one hat fits inside the other and is nice and warm!
You need to keep track of your rows to make it the same size. I don't know of any adult double hats or double knit patterns though. :thinking: If you want it beanie style you would just make it shorter I think...