Reupholstered Older Womb Chair. Is this Knoll fabric?  

It's a hopsack weave, so that's authentic, at least. I can't tell from your photos what the exact color is so I can't help with that. But it doesn't look even close to any of the current colors of Knoll hopsack but it also kind of looks like maybe it's nylon and not wool, so that would rule out the Knoll wool hopsack. BUT---there's also Alexander Girard hopsack which is/was all nylon. There's a color chart of this stuff floating around the internet if you can find it.

I wouldn't worry about it a whole lot, though. It looks expertly done and a hopsack weave is 100% correct. Unless you can confirm the fiber content* and get an exact color match, it could be tough to pin down the ID.

(Knoll changes their colorways every now and then. Also, their wool hopsack does not look too durable to me. I have some in several colors and it has a very thin, lightweight, soft feel. If you can snip a few threads of the fabric from the underside, you can do a burn test---wool smells like singed hair and leaves a black bead of ash that is easily crushed. Nylon melts; some people say it smells like celery. Polyester burns fast, melts and leaves a gooey blob; has a chemical odor. Blends are harder to figure out.)

Spanky, that was incredibly helpful! I didn't know that the weave was called hopsack, or that hopsack is authentic for a Womb Chair. The fabric is either nylon or polyester, and the color is very hard to photograph. In brighter light and in natural sunlight, it does resemble an Eames sofa in Girard Midnight Blue that I found online.

Also, do you, or anyone here know when the plastic feet were used? I've done a lot of looking around here, and can only find info on the earliest feet, and the later ones. Thanks again!

Also, here's one of the glides I was referring to, and a pic of the seat cushion. The thickness is measuring around 4.75" thick. Does that seem right?

I don't know anything about the glides--sorry.

I don't know what the seat cushion thickness is supposed to be but a photo of the chair from the front will make it easier to determine if it's close or not. I would just compare it a photo of a new one.

The fabric looks like a synthetic for sure. Did you try burning it? Do it over a candle flame rather than a lit match---that way there's no burning sulphur smell to mask the odor of the melted fibers. (Just don't use a scented candle!)

4.75" seems too thick. My Womb chair and settee have 4" cushions.

Both pieces have been reupholstered, but they were done by different upholsterers who were told to use Knoll's original dimensions, so the fact that they both ended up at 4" leads me to believe that that was the Knoll spec. Plus, they look just like the original-upholsterychairs I've seen in person and the original-upholstery settees I've seen in photos.

Womb cushion thickness came up once before: https://www.designaddict.com/comment/133029#comment-133029