The PHFS-01e is a heat flux sensor that is encapsulated in either copper, brass, or aluminum in order to make it more robust. The metal encapsulation may add a relatively small amount of thickness and thermal resistance to the total sensor package, but it also allows the PHFS-01e an increased sensitivity and durability. Increased durability is advantageous when the sensor is required to withstand removal and reapplication to measurement surfaces multiple times throughout its lifetime.  This sensor is NIST traceable.