Injection molded soles

How to Identify injection molding

It is not so complicated - after the boot manufacturer makes the "uppers of the boot" they place these boot "uppers" in a metal mold and inject molten plastic into that mold forming a bottom. This becomes the sole, or the "substrate" in which the sole is mounted. The sole unit never actually exists as a seperate part from the boot.
    
Notice the fine vertical lines in the plastic. These "parting lines" are from spewing of the molten plastic between the metal mold sections used to form the soles. These lines are typical and though not always as obvious as in these pictures, can be found center toe (below) and center heel (above) in the plastic material below the leather upper .
   
Above are examples of mold parting lines in the toes of two boots.
Below shows how substrate bled through the stitch holes in the "inseam"
    

Another telltale sign of injection molded soles

The above view looks down into the boot from above the ankle, footbeds removed.
See the stitches in the bottom around the perimeter of the insoles? Many of the stitch holes show little bits of plastic which bled through. The molten plastic is injected into the molds under pressure, so can "bleed" through these stitch holes.