I occasionally get asked why modern synthetics are so much better than the dreaded polyesters of years gone by. Here's (a simple version of) the story ...

As applied to fabrics, "synthetic" is simply a marketing word meaning "plastic" (albeit many different kinds of plastic: rayon, nylon, etc.). In order to weave fabric from it, the plastic is melted and extruded through a tiny hole to turn it into a thread. In the old days, this was the extent of the process, so the resulting "thread" was like a solid piece of spaghetti (though much thinner), had no real texture, and felt like what it was: soft plastic.

"Real" fabrics, on the other hand, are woven from natural materials (cotton/wool/silk spun into thread, for example), and this yarn is neither solid nor texture-less: there is a great deal of entrapped air, and the thread is "fuzzy", not smooth.

In recent years, improved manufacturing technology has enabled the creation of synthetic yarns with these same characteristics; they can be hollow (with multiple chambers), fuzzy, crinkled, etc. This has allowed the weaving of fabrics that have a combination of desirable features: quick drying, abrasion resistant, wrinkle resistant, able to wick moisture efficiently, and having a good "feel".