where {displaystyle R_{0}} R_{0} is resistance at temperature {displaystyle T_{0}} T_{0}. Therefore, many materials that produce acceptable values of {displaystyle R_{0}} R_{0} include materials that have been alloyed or possess variable negative temperature coefficient (NTC), which occurs when a physical property (such as thermal conductivity or electrical resistivity) of a material lowers with increasing temperature, typically in a defined temperature range. For most materials, electrical resistivity will decrease with increasing temperature.