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If two identical electrolytic capacitors are connected in reverse series, then at sufficiently low voltage, they should effectively behave as two simple capacitors, which leads to a reduction in capacitance by half (such as simple series connection) relatively to sufficiently large voltage (in which the reverse capacitor is equivalent to a short circuit). The text "Non-polarized electrolytic capacitors (which effectively are two polarized capacitors placed back-to-back)" is at Digikey. Will the capacitance of a non‐polarized or bipolar electrolytic capacitor significantly decrease at sufficiently low voltage?

How does the capacitance of non‐polarized or bipolar electrolytic capacitors depend on DC bias voltage?

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It doesn't really have much effect. And all aluminum electrolytic capacitors are bipolar, just not necessarily symmetrically.

A regular electrolytic capacitor has a relatively thick oxide layer on one side of the foil (the anode) and an extremely thin layer on the other (the cathode). When polarity of applied voltage is correct the thick oxide blocks the voltage and the thick oxide also dominates the capacitance. If you reverse the voltage, however, the capacitor can only withstand a volt or two before it starts to leak. Image from Wikipedia:

enter image description here

A bipolar capacitor looks almost identical inside at first glance, but it is made with thick oxide on both sides of the foil, so either side can be the anode. The trade-off is that the capacitor has to be about double the volume for the same capacitance because you now have two thick oxide layers in series and that (approximately) halves the capacitance, all other things being equal.

Here is the voltage coefficient (typical) of an ordinary electrolytic capacitor from this source:

enter image description here

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  • \$\begingroup\$ Halves the capacitance is counterintuitive and not obvious. If, during the flow of reverse current through a (polar) electrolytic capacitor, the voltage on it increases to a few tenths of a volt, and then it turns into an almost infinite capacitance (before its destruction). Then why does each oxide layers of a non‐polarized or bipolar electrolytic capacitor in both voltage directions create a capacitor with almost constant capacitance up to the half rated voltage? \$\endgroup\$
    – Imyaf
    Commented Sep 27 at 19:14
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    \$\begingroup\$ There's twice the total thickness of dielectric so the capacitance is half. Two polar capacitors in series will develop a voltage at the midpoint that you can evaluate and again the capacitance is halved. \$\endgroup\$
    – Spehro 'speff' Pefhany
    Commented Sep 27 at 19:20

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