A Hot Runner Mold is similar to a hot glue gun.  Material heated to a molten state,  then it  is dispensed at the tip to the desired area.  Hot Runner Molds have many unique advantages over "Cold Runner" molds.

While Hot Runner Molds are typically more expensive than a "Cold Runner" molds, the cost of the mold  can be offset in other ways.  Thermoplastic  Hot Runner Molds can reduce costs by the following :

 No scraping of the the runner.  As the term implies, the runner in a Hot Runner mold  stays in a molten state at all times.
        No Removal of the Runner from the part  (Labor)
        No Regrinding of Runner (Labor and material handling)

 Processing Advantages (hot manifold vs cold sprue):
        Lower Injection Pressures
        Clamping Pressure is lowered
        Consistent temperatures in the cavity
        Cooling time reduced
        Shot Size reduced by amount of runner volume
        Elimination of Nozzle freezing 
   
Reducing the cycle time.  In a Cold Runner mold the runner typically has the largest cross sectional area, therefore, the runner takes longer to  solidify.  Eliminating the runner reduces the overall cycle time.  Furthermore, injection time is reduced due to the shot size being  reduced by the elimination of the runner.