The short answer: Some local stores will tell you nylon's better, no matter what, and I'm not sure I fully agree with that. Every fiber type has its positive characteristics and its drawbacks. There's no perfect fiber. Today's nylon has been made much softer, and a well-made polyester, something with a good twist and decent density, is going to wear similarly to a nylon carpet that's been softened. Polyester is also very stain-resistant, takes color beautifully, and pound for pound tends to cost less.
How has nylon changed?
Nylon, at one time, was very good for wear and for resisting matting and crushing, but it wasn't very stain-resistant. Then in 1986, Stainmaster was developed. Stainmaster was essentially a clear dye. They would dye the color into the fiber, and then they would clear coat it. That's what provided the stain protection.
At that time, the denier of the yarn was quite thick. Denier refers to the actual thickness of the fiber, if you looked at it under a microscope. That old nylon had a very wiry, rough feel, but that thick denier and that feel are what gave it its durability.
As time has gone along, people's preferences have changed. People now prefer carpet to be a lot softer, and the manufacturers all know this. So what they've done is make nylon softer. To do that, they made the denier smaller and finer, almost like cotton candy, or something extremely fine, like silk. That has made nylon softer and closer to the feel of polyester. But because of that, they've sacrificed the chunky durability you used to get with the old, bigger-denier nylon.
A story. One of the local dealers bought some very high-end soft nylon carpet from one of the major manufacturers. It was over $40 a square yard. After 2 years, he pulled it out and replaced it. It just hadn't held up the way he thought it would. That's because they softened the nylon in a way that made its performance much closer to what you'd get out of any other soft fiber.
What about polyester?
There are different grades of polyester, and the polyester fiber used for carpet is made at the very highest grade and level that polyester is made.
It's very stain-resistant. Just imagine a pop bottle. Can you stain the inside of a pop bottle? No, you can't. That's because the chemical structure of polyester is much tighter than nylon, and it's just naturally impervious to staining.
It's soft, and that's where its reputation comes from. Most polyester being made now is quite soft, because that's what people tend to want. That's why polyester gets a reputation for not holding up quite as well. But again, it boils down to trade-offs. The manufacturer has decided to make the carpet softer because that's what people want, at the expense of long-term durability.
It takes color beautifully. Polyester dyes very well. You get really pretty colors with polyester that are just hard to duplicate in nylon.
It costs less. Pound for pound, polyester tends to cost less than nylon. That's one of the reasons you see a lot more polyester carpets right now than nylon.
Another story. When we bring in rolls of nylon carpet and show them on our floor, we have a difficult time selling them. They don't look as pretty, they don't dye as well, and they have that old, rough nylon feel. When people feel them, they don't like them.
The bottom line
There's no perfect fiber. Well-made polyester, something with a good twist and decent density, is going to wear similarly to a nylon carpet that's been softened, and it's prettier and costs less.
People also plan on changing their carpet more often than they used to. They don't expect to squeeze 30 years out of carpet like they maybe would have in the '70s or '80s. People know products don't hold up as long now, and they're looking more for softness and how pretty the carpet is. (See How Long Does Carpet Last?)
Want to feel the difference for yourself? Come see us in Provo or Lehi.