Polyester, a man-made plastic, is employed in pillows in two different ways. What most people mean when they refer to "polyester pillows" are pillows stuffed with polyester fibers, of various thread counts, higher thread counts making for better-quality pillows. The critical consensus about these types of polyester pillows is that they are merely mediocre. They are inexpensive, yes, but they also offer only average neck support and are prone to develop lumps and hollows after a relatively short time. On the plus side, polyester-fiber pillows can be more durable than other types; SleepLikeTheDead.com concludes, "At a low price, they can be considered a fair value since they will likely last at least a few years."
The other, less common type of polyester pillows are pillows filled with polyester gel that simulates the feel of natural down. These synthetic down pillows get the nod from editors at Real Simple magazine, who say they "mimic the down pillow's ability to flow around the neck and head...the material is hypo-allergenic, which is great for sleepers with allergy problems." On the contrary, consumers posting reviews at SleepLikeTheDead.com are every bit as blah about gel pillows as they are about ordinary polyester pillows, with the additional disadvantage that (when new) these pillows can emit a chemical odor. Polyester gel pillows score best for their light weight, easy maintenance, and down-like comfort.
You should also bear in mind that polyester tends to absorb sweat, facial oils, dead skin cells and the like more readily than other kinds of pillow fillings, meaning you'll have to clean these pillows regularly. Allergy sufferers may want to consider other kinds of pillows instead.