Shoes That Wear Themselves Out Just Sitting in the Closet.

Note the crack at the base of the heel but no noticeable
wear on the walking surfaces of the sole.

      The other night I noticed dirt on the tile floor of our laundry room.  When I tried to pick it up it just crumbled in my hand.  So, I got the Dustbuster and vacuumed it up.  As I looked to see if more dirt was about, I noticed that more dirt was being deposited with every few steps I took.  Dang.  I must have picked some mud up while I had gone out to get the mail.  I looked at the bottom of the shoes and realized it wasn't dirt but rather that the heel of the shoe was disintegrating.  It was not dirt but really crumbly rubber.
     I was a little annoyed because, while these shoes were several years old, I did not wear them that often.  There was no reason, or so I thought, that the sole of the shoe should be deteriorating in such a manner.  I googled Ecco, the name of the shoe company, and "shoe sole disintegrating."  There were plenty of consumer complaint sites documenting the exact problem I had experienced.  This was a known issue.
     I called Ecco customer service.  While they did not acknowledge any ongoing problem, they quickly said they would be send out a postage paid envelope that I could use to return the shoes to them.  I was told they would evaluate the issue.  If deemed their fault, they would either send me a new pair of the same shoe or a credit to buy another pair.  That sounded fair.  I figured that even though the shoes were old, I rarely wore them and when I did I wore them on dressy occasions when we had company.  I rarely wore these particular shoes outside.  
     I asked if the shoes could be resoled and that would be fine with me.  The agent said that this was not possible because the sole and heel were made polyurethane which was molded right onto the shoe.
     This was not the first time this happened to me.  The same thing happened last year with a pair of Blundstone boots that I had bought in the early 2000s for snowy days.  The soles of these boots disintegrated in almost the same way.  It was in my office and again, at first, I thought it was dirt.  Those boots had to be thrown out as they couldn't be resoled either. In this particular occasion, I just assumed that the rubber (I did not know they were polyurethane at the time) dried out with age and began to crumble.
     I ran across a website that explained why my initial theory was wrong and why this phenomena actually happens:

The shoes had a moulded polyurethane (PU) sole, which, while being light and comfortable, is prone to a form of deterioration called “hydrolysis”, especially in coastal, humid areas, when not worn. In short, they crumble into a sticky mess.

It seems the act of wearing them puts pressure on the soles and squeezes out the moisture, which would otherwise insidiously break apart the foam-like structure. So it’s possible for a pair of unworn or barely worn shoes to disintegrate.

As I discovered when I Googled the words “PU soles” and “disintegrate”, this is a hot issue, and affects most brands of “comfort” shoes, among them Clarks, Hush Puppies, Green Cross, Scholl, Bass and Ecco.
~ IOL a New Zealand News Site

     Basically, shoes with these kinds soles, which indeed are light and very comfortable, last longer the more you wear them and they wear out faster if you don't.  That sounds oxymoronic.  I will have to remember this if Ecco sends me another pair.