The reactance of capacitors increases as:

Capacitive reactance is the opposition a capacitor presents to alternating current. The mathematical formula for capacitive reactance is X_C = 1 / (2πfC). Because frequency (f) is in the denominator of the fraction, there is an inverse relationship between frequency and reactance. If you want the reactance to increase, the frequency must decrease. Applied voltage does not change the physical property of reactance. The reactance is strictly a function of the capacitor's internal value and the frequency of the AC signal passing through it.