USPS Foam Shipping.
When you choose USPS shipping for your Foam of your box kit you will have two shipments. One by FedEx that will have all your boxes. A second shipment will go out with USPS and have all the foam for your boxes. Were offering this to save you money on shipping cost. You have to understand thought that USPS can sometime take longer for your packages to arrive. So if you are in desperate need on the complete kit you should stick with the standard shipping. If you have time and want to save a few dollars then pick the USPS option.