Some terms and a bit of history..
First there are more that two types of low ESR caps used in PCs.
Aluminum Electrolytic, Solid Polymer, Hybrid Polymer and Tantalum.
Hybrid and Solid Poly caps performance longevity and all that are so similar they are considered the same thing even though structurally they aren't.
Few people outside the cap manufacturers themselves even realize there is a difference.
So when you see "Poly" or "Solid" or "Solid Polymer" it usually means both or either polymer type.
Tantalum were experimented with by multiple manufacturers and ultimately rejected for most PC applications because they don't tolerate ripple very well and tend to die young. They did (and might still) see some use in laptops because they are small and the nature of laptop power bricks is such that they aren't exposed to more ripple than they can handle. There are 'wet-tantalium' and 'dry-tantalium'. Wet-tantalium fell out of favor in IT equipment quickly because their electrolyte is highly acidic and will eat just about anything it leaks on to. If you have a leaker gloves are a good idea.
Aluminum Electrolytic ["Lytics"] (the most commonly used type before 2010-ish) have wet electrolyte on both plates.
Unfortunately many of the best choices for replacements are no longer manufactured.
Early on these were the only practical choice. Poly had limited uF capability and were very expensive.
Lytics could simultaneously get the ESR low and pack enough uF into a small enough package to avoid needlessly wasting space.
They are also resistant to damage from ripple.
Solid Polymer. Have polymer electrolyte on both plates. (Basically a kind of soft non-hardening plastic.)
They were invented by Sanyo who by way of patent rights was the exclusive producer until some time in the early 2000's.
Sanyo's trade name for their solid polymer caps is OSCON.
Initially, due to tech limitations, OSCON were only available in small sizes (like 330uF or less) and were physically large for their uF value.
In the 1990's a single 330uF OSCON could cost you $30 so they were not common.
Eventually the tech limitations were overcome and and patent rights ran out.
Now Solid Poly caps are made to much larger uF values but the larger ones are still more expensive than other options and actual OSCON are more expensive than other brands.
Hybrid Polymer. [aka Functional Polymer] Have polymer electrolyte on one plate and wet electrolyte on the other.
Invented by Fujitsu to compete against OSCON. - Functional Polymer were cheaper to produce.
Fujitu's trade names for the product were "Functional Polymer" and/or "FP-Cap" or "FPCAP".
Fujitsu only retained exclusive rights for a short time before licensing the right to produce to other companies.
This busted Sanyo's monopoly and is the main reason polymers started getting cheaper in the early 2000's.
Just few years ago Fujitsu sold the subsidiary responsible for FP-Caps to Nichicon.
At this point Poly's are only slightly more expensive than Lytics in most sizes and in some cases (high production sizes) can even be cheaper.
GRUMPY OLD FART - On Hiatus, sort'a
Mann-Made Global Warming. - We should be more concerned about the Intellectual Climate.
You can teach a man to fish and feed him for life, but if he can't handle sushi you must also teach him to cook.