When designing a pagewide thermal ink jet printing system you can use one of three different engine architectures. The first is “design for width” where individual silicon die are assembled into a monolithic printbar which is wide enough to print on the media size you are targeting. HP's OfficeJet Pro x uses this approach, and it provides the smallest and least expensive path, but it gives you no direct flexibility in print width. The second architecture stacks monolithic printbars into a wide array like you would stack bricks to make a wall. While this provides media width flexibility, it creates a much wider print zone where you must keep the media flat, and a bigger zone where you must maintain absolute position and velocity control. Even then there will be artifacts created between the staggered printbars caused by differential drying time. And of course the printer itself becomes larger. But this system can allow you to bring large products to market quickly, and HP has done this with its family of ink jet based web presses. The third method involves designing a nestable module, several of which can then be assembled into printbars of various lengths, from an office printer size machine up to the 40 inch print swath recently introduced on the HP pagewide product. This approach combines the low cost of architecture 1 with the flexibility of architecture 2. And since each module is individually replaceable it is more convenient for the customer as well. This paper focusses on some of the benefits and challenges of the nestable design.