On 22/11/16 12:53, rick wrote:
On 22/11/2016 10:40, wrote:
On Tuesday, November 22, 2016 at 9:02:10 AM UTC, Brian Gaff wrote:
Heat and cold cycling in the place where it lives?

Are they rubber, or are they polyurethane? If it's polyurethane it could
be hydrolysis, the process that makes shoe soles fall apart when used
after
a long period of storage - happens a lot at weddings apparently.

I bought a proper dust mask last year, used it a bit then put it in
the shed.
When I got it out last week the elastic in the strap had totally crumbled
into black dust. The rubbery bit that fits on the face looked good as
new.


The appear rubber .. but I can't be sure.

I know what you say, I had 2 pair of Army boots - put away in cupboard
and the 'Tuff' soles completely deteriorated .. went very soft and
pieces falling off.

Have non-MOD walking boots over 25yrs old with Vibram soles and they are
still going great.
MOD buying to a bargain price I guess.

Its more about expected use. The average lifetime of a Supermarine
Spiftire was about 30 operational hours. There was very little point in
making it out of stuff that lasted longer.

Nor in making the engines last much longer than that.



--
All political activity makes complete sense once the proposition that
all government is basically a self-legalising protection racket, is
fully understood.