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 pleasant "feel".