What circuit parameter change causes an inductor's reactance to increase?

The inductive reactance of a coil is determined by the formula XL = 2πfL, where 'f' is the frequency and 'L' is the inductance. Because frequency (f) is a multiplier in this equation, inductive reactance is directly proportional to frequency. Therefore, as the frequency of the AC signal increases, the inductor's opposition (reactance) to that specific signal also increases. This is why inductors are often used to block high-frequency noise while letting low-frequency or DC signals pass.