Let me chime in:
I agree nylon is the strongest fiber used to make carpet, and therefore results in the longest wearing carpets. 80 percent of commercial carpets are made of nylon fiber.
The problem, however, with nylon is that it's got polar groups on it, which makes it highly susceptible to water based stains. DuPont has spent a king's ransom trying to make their "Antron" nylon more resistant to water based stains, and they're still trying.
There is a certain wisdom in knowing when to give up.
Other producers of nylon are now producing "solution dyed nylon fiber" and are selling it to make commercial carpets out of. That way, you have the durability of nylon combined with the ability to use bleach or acetone straight out of the jug on the carpet to remove otherwise impossible stains.
For those who don't know:
A "solution dyed" fiber is one in which the fiber is coloured by adding solid coloured particles called "pigments" to the plastic before drawing it into a fiber. As a result the coloured pigments are encased in the plastic fiber very much like raisins in an unsliced loaf of raisin bread. Since the colour of the carpet comes from the pigments, which are encased in nylon plastic, you can use strong chemicals like bleach to remove any stains from the exterior surface of the fiber without discolouring the pigments encased inside the fiber.
That way, you can have the durability of nylon with the ability to use bleach to remove stains from the carpet fibers without bleaching the carpet.
If someone in here doesn't think that's an important selling point, they come from a different planet.
PS: I've been using bleach to remove dyed candle wax stains from Olefin carpets for about 22 years now. (Tenants love candles.) There's a supposed carpet cleaning guru who works out of the place where I buy my carpet here in Winnipeg, and he warns against using bleach on any carpet. He said it would "etch" the carpet fiber, making it rough. I asked him if it did that, wouldn't that rough surface scatter light, making the carpet look whiter? He couldn't answer that. Think about it. If you take a piece of sandpaper and roughen up any smooth surface (even glass), those scratches will look lighter in colour than the original surface because they're rough and scatter light in all directions. Light coming from all directions reflects and refracts off that rough surface and when it refracts, the different frequencies of light get scattered in slightly different directions (just the same way as a prism works). Your eye sees the combination of different colours from a rough surface as the colour "white". So, if you scratch a piece of glass, the scratch with be white. If you've ever seen heavy machinery scratch concrete, the resulting scratch is white. Even if you scratch a black granite tombstone, the resulting scratch will be a whiter version of black. If bleach were to cause any increase in roughness of the surface of the carpet fiber, you'd expect to see a whitening of the carpet (even without any chemical "bleaching" effect) just due to the roughening of the carpet fiber. Therefore, if you don't see that, then the bleach is not affecting the smoothness of the carpet fiber.
PS2: As I have typed this post, I have had a scrap piece of the solution dyed nylon carpet I installed in Suite 2 sitting not more than 4 feet from me with some undiluted bleach soaked into an area the size of a quarter. So far no detectible change in the carpet colour, except that it is darker, as most water absorbing materials are when they're wet. I just now used a wad of toilet paper to wick up that bleach, and there is absolutely no discernable change in the carpet colour whatsoever. And, it's taken every bit of 10 minutes to type this post so far.
The carpet I installed in Suite 2 and tested the bleach on is made by Shaw. It is their "Franchise" line of commercial level loop carpet. The colour I purchased was #10405 called "Starry Night", but all of these carpets in the Franchise line are solutiond dyed nyon and would not be harmed by bleach.
A second 100% solution dyed nylon commerical level loop carpet made by Shaw is their "Reward Power" line.
Tigerbalm: You have very little to lose by spending $2 on a car floor mat size sample of a 100% solution dyed nylon carpet and torturing it with bleach. Just look on the back of the sample and it'll say what fiber it's made of, and if it's nylon, whether or not it's solution dyed nylon.
Just pour some Grape Kool-Aid (worst stain I could think of) on the sample, rub it in, and use bleach to remove the stain. Just apply the bleach right out of the jug to the stain, allow it to work and remove the stain, and then suck the bleach out of the carpet using the suction hose of a wet/dry Shop Vac vaccuum cleaner. Just press the end of the hose down on the carpet and the air flow will pull the bleach out. Then apply clean rinse water several times, recovering the rinse water after each application. Maybe try a good grade of water based wood stain on the carpet, too!
If you have a puppy or kitten, you can also use bleach to kill any germs (disinfect) on the areas of your carpet where your puppy or kitten had an "accident" exactly the same way. That way if you have a toddler dropping things on the carpet and then putting them in his mouth, you don't have to worry (as much) about what he's puttin in his mouth.
In my books, not having to worry about staining a brand new carpet because you can remove that stain with bleach is an important selling point that no one seems to have mentioned so far.
PS3: I have no fight with foam chip pads, but I install a 38 pound commercial pad called SP380 (I don't know who makes it) in every apartment in my building, and I've had absolutely no problems with it. It's strong ad thick and seems to last forever. When I remove the old carpet in a suite, I press down on the traffic lane and compare how it compresses with the non-traffic areas in the corners of the room. Until I start to detect any difference, I'll keep installing new carpet over the same SP380 solid foam rubber underpad.