I sort of unfairly handwaved the durability issue earlier. I maintain that synthetics, strictly speaking, are more expensive per gram (& often per thread). But if a synthetic material is X times more durable than the natural material it replaces, & only Y times as expensive (in sustainability terms), and X > Y, then there could be an energy savings per use.
This requires energy savings through making fewer replacements. Economically, the savings will require lower production & lower consumption–implying a need for a higher price per piece. Someone who wants a wide variety of outfits in different colors, or who replaces clothing every year as a matter of trend-following, would not be saving energy unless their non-synthetic clothes wore out much more quickly.
Also if the material tears irreparably due to trauma & must be replaced, or is discarded due to contamination, the energy gain goes away.
Even if we embrace this model, the question becomes, which synthetics are more durable? There are different reasons for choosing synthetics:
Some synthetics have been embraced as cheap alternatives to bio-polymers. E.g., polyester & nylon both substitute for imported silk. Of course, there’s no reason in theory we couldn’t just import & mass produce silkworms, & the calculus would change.
Synthetics may also appeal because the chlorination process (or other chemical process) makes them unattractive to pests & slow to biodegrade. But they are not necessarily stronger. From a waste-stream standpoint, this is actually a negative, because they become far less compostable. Further, the chlorinated compounds can’t be burned without creating dioxin pollution.
A few may actually be stronger & more tear-resistant than their likely natural alternatives (though this depends on “likely”; a heavy zoo-polymer fabric–like silk or a gut derivative–can actually be quite tough, & would be hard to beat).
So you see, if cheap mass production or resistance to moths is your criterion, then you still may not be getting more strength from synthetics.
That said, I think polyester is durable enough to be worth it–except for the massive waste-stream headaches. Getting used polyesters into a recycling stream is not easy, or even likely in the present culture. (Also, it’s not as comfortable as linen or silk, imo.)
Also, some materials end up being replaced not because they wear out but because they are discarded due to contamination. Oddly, in this case a plastic may be desirable because it can be made waterproof easily. And in some cases, you can make it thinner & get energy savings that way. Think of surgical gloves.
Even non-disposable plastics are interesting because of their ready waterproofability. But other than rain gear & the plastic covers for cloth diapers, who wants to dress in thin plastic?