The insole is the platform between the footbed and the midsole. The purpose of the insole is to provide a stable platform for the foot, which is a key factor to stability and forefoot flexibility. It is also the surface that joins the upper to the bottom of the boot and keeps the components of the bottom working together.
Take a look at the diagrams below to gain a better understanding of the insole and its functionality, as well as to see a visual depiction of where the insole is located in the construction of the boot. Red Wing Shoes offers an extensive line of footbed upgrades for additional comfort and support.