Womb Chair, Egg Chair, Swan Chair...etc.  

I wouldn't call it a "major design flaw"
but yes, the original foam in a forty- or fifty-year-old example of any of those chairs will have disintegrated by now.
If a chair's design calls for the fabric to be laminated to the foam, it is not cost-effective to separate the two and relaminate old fabric to new foam.
All of my really old fabric-upholstered pieces -- Bird, Cones, Womb chair and sofa, etc. -- have been reupholstered, and they're all nicer now (and more valuable, if you care about that) than with their old foam and fabric.
Leather is maybe a different story, but unless your old leather is completely intact and you're working with something like an Egg, you'll spend way more than the chair is worth trying to reuse it. And I think you're right about reshaping the leather a second time; that doesn't look as though it would be easy. I wouldn't even bother trying with anything less valuable, like a Swan or Womb.

You can still get some of
those original fabrics, if that helps.

I agree with fastfwd
... in that it is not a major design flaw. When these pieces were designed, they were created as furniture to be used. Not artworks, collectibles or museum pieces. That they have attained that status is our response to them over time, not the designers intent.
While it is pretty much inevitable that the foam will be petrified if the chair is upholstered in fabric which is breathable, if it was originally upholstered in leather or vinyl, you might be surprised how well it has held up. It's the exposure to air that causes the foam to oxidize. I have an egg chair from 1960 upholstered in vinyl that is in excellent condition with no discernible hardening to the foam. We also recently acquired a first generation 1958 egg chair in original leather, the original version without the seat pad that is also in great shape. There is a couple areas where the foam has hardened, but overall it's very good. I think of this chair as a museum quality example. I expect a serious collector would want to keep and use this as it is despite the slight hardening as it barely effects the appearance and does not effect the comfort or usability of the chair at all.
However, if they decided that the foam needed to be soft, supple and perfect everywhere like it was new, I think that the chair could also be restored without effecting the value one bit. On the egg chair, the foam is on the front with the back being covered in a dense felt. The leather on the front of the chair could be taken off, the foam replaced, and the original leather re-applied. It would not be inexpensive. I would expect to pay about $1500 to have it done, but considering the value of the chair, not unreasonable to spend.
It's uncommon for the fabric on a very old chair to not be dirty or damaged beyond repair, and most times it needs to be replaced. If well done in an appropriate fabric or leather, reupholstery does not diminish the value. In fact, it generally increases it. We have had many fabric covered chairs reupholstered. In fact, we just had a very nice early womb chair reupholstered for a customer in Hallingdal 65. We have also had on a few occations chairs restored, saving the original fabric. I shared the story of our restoration of a first generation swan chair with wood legs in this thread:
http://www.designaddict.com/design_addict/forums/index.cfm/fuseaction/th...

I have a France & Søn sofa
That dates to sometime between 1960 and 1964. The wool upholstery was trashed (very, very stained), but the foam inside looked as good as foam from 10 years ago. And the upholstery and foam was all original, it still had France & Søn production tags in the airspace where the springs are.
I was very surprised at this discovery, as my expectation was that the foam would have been completely shot.
In fact I am sitting on it now.
There were some Eric Buch chairs bought at the same time from the same sale, and the foam seats had become powder.
So, there is more to the story than just age. And foam can survive even with fabric upholstery.
And I don't pretend to understand how the foam in this sofa survived. If I had to speculate, I'd speculate that no one had sat on the sofa in decades, unlike the chairs, and the compression and expansion of the foam sucks oxygen into the foam, which causes the degradation.
But since that is just idle, baseless speculation, I am just putting it forward as one example that shows that it is possible for 50 year old foam, stored in a living room, wrapped in fabric, to be in fine condition.

poor choice of words
DavidR,
I would not be surprised that a "60's womb chair or egg chair today with the original fabric or leather" required parts replacement and maintenance during a 50 year time span.
Saying these "designs all have a major flaw" is most certainly a poor choice of words. You may be experiencing the very same "flaw" with the soles of your shoes.

Leif
Did your sofa have latex foam? I've seen original urethane foam in furniture dating to the 60s, which is why I ask.

Leif
Did your sofa have latex foam? I've seen original urethane foam in furniture dating to the 60s, which is why I ask.

You're right spanky
Both times you said it.
I have as well, and I suspect there is some validity in leif ericson's notion of use (compression) as the pieces I've had where the latex foam was still good were in pieces that were very gently or rarely used.
We have a Nelson loose cushion lounge chair and ottoman from the 1950s. Both the fabric and the latex foam are original and in excellent condition. All we did to restore it was to tighten the webbing in the seat deck.
You'l note that I did not make a definitive statement but said "pretty much" because the vast majority of vintage upholstered pieces we've handled showed some signs of hardening foam if not completely petrified.

I've also wondered if
some latex was cooked a little differently and maybe had some other qualities that made it longer-lasting. I've seen it in so many states of deterioration. It is made from sap of living trees and there's no way that that can be totally uniform from grove (?) to grove, year to year, even tree to tree. And certainly the processing isn't a strict science. It just stands to reason that some latex foam will last longer than other latex foam, even without factoring in all the other stuff regarding use, storage, room temperature, etc.
Oh, and there are those awful clear vinyl slip covers that were popular back the day. I bet they helped a cushion or two stay nice far longer than they would have if left nude.

Niceguy,
While I do respec...
Niceguy,
While I do respect your opinion, I would not call it a poor choice of words at all. Needing parts replacement and maintenance during a 50 year time span is to be expected. The Eames lounges are great, for example, because the most common repair is the shock mounts. Those can be sent to the manufacturer and replaced for 400 dollars (relatively reasonable). If cushions are needed, vintage sets can be found on ebay and easily swapped. The lounge can then be passed down from generation to generation, ideally with 90% of the same parts as when it was new as long as it is properly maintained. The womb chair and egg chair on the other hand are sought after because of the iconic design and often uniquely beautiful wear of the upholstery. After 40-50 years, you are not simply replacing parts, you are replacing the majority of the chair aside from the structure. It is a characteristic that prevents these chairs from getting better with age. What about a 60 year old reupholstered egg chair has gotten better with age? If the foam has gone and upholstery was replaced, you have destroyed the patina (just as it reaches it's prime).
Could Fritz Hansen and Knoll make these chairs with any other foam material that would not disintegrate over time?
Basically, this post was partially posted because I wanted to lament about the loss of so many beautifully upholstered examples. Every original leather egg chair that had perfect leather and terrible foam is seen by myself as a great loss to the collecting/design world. The egg, womb, and swan are done by highly skilled workers, who do the best job of executing the original intended design. To see their hard work destroyed because of degrading foam is a shame.
Imagine sacrificing a beautiful cognac leather egg chair because the foam has turned to dust. I would be on my knees with tears falling.

Urethane vs latex
Spanky: I don't know whether it is urethane it latex. I must confess I don't know how to differentiate. I'd be happy to open one up and examine it howsoever you suggest.

But
it's furniture, meant to be used and enjoyed. Even the best wool fabrics have a limited lifespan unless no one ever uses the furniture, and then what's the point of having it? There isn't any foam that will retail its resilience forever, either. Cotton upholstery batting absorbs household odors and humidity and gets old-smelling. Nothing is permanent, in other words.
What I have come to despise is upholstered furniture that wasn't designed to be reupholstered. THAT is poor design.

Latex weighs a lot more
than urethane foam per the same mass. It also has a lot more bounce even when it's old. It feels rubbery.
Urethane foam has less resilience, less bounce even when it's brand new. It just has a very different quality than latex foam.
Urethane foam will eventually develop hollows where people sit, lay or lean on it. Even the best quality urethane foam will break down eventually. Latex doesn't, at least not to my knowledge. It will get dried out where exposed to air but the layer under the dried-out top will still be bouncy.

DavidR
When you say that old chairs with original upholstery have "uniquely beautiful wear of the upholstery" and that 60-year-old upholstery has "patina" that's just reaching its prime, you're talking only about leather upholstery, right?
Because I don't know ANYONE who thinks that worn, soiled fabric upholstery is desirable.