Need a replacement sanding pad for a Festool 125 EQ 5" sander serial number 13011376.  Tried the spare parts look up, but not clear which pad fits my sander.  I live in Florida and the heat and humidity completely destroyed the foam in the sanding pad.

Thanks Alex.  I looked at this one, but not sure it would fit since I could not find ETS anywhere on the sander.

https://www.amazon.com/Festool-492280-Jetstream-Replacement-Sanding/dp/B002VMVG76

It is not the heat and humidity of Florida that destroyed your pad, they deteriorate on their own due to the chemicals used in it.

Really? I have never heard this before. How long does this typically take?
My original RO90 was well over 5 years old and before the fire killed it, had never showed any signs of deterioration. The ETS EC 125 was only about 2 years old then too. I didn't use it as much as the new one I have now, but if time is the factor, that shouldn't matter that much.

Also…I think if you are sanding (just about) “anything” or say a painter, the pad gets exposed to a lot of “stuff”…as compared with use in strictly say, a cabinet shop, where it’s only sanding new wood

The disintegration issue has happened to me with Festool, Dewalt, Milwaukee and Porter Cable. The interesting thing is that the oldest sander I own, a National Detroit DA that's over 40 years old is still fine. 

I've got pads from sanders I've personally had for 20+ years and ones I've inherited even older. Never had this problem of them spontaneously decomposing. Maybe it happens with some or certain compounds but I wouldn't think of it as an inevitable conclusion for any and all pads. Environment will definitely have an impact too, warm damp/humid climate will cause anything to decompose faster than a colder and drier one. That's just basic physics not unique to sanding pads.

I've had sanders from Rupes, Metabo, Bosch, Black & Decker and Festool. And it only happened to me with the Festool sanders, and with lots of them, the RO150, ETS 125, DX93 and RTS400.

I had one sander of Black & Decker, and I only had to replace the pad after 16 years because I made the mistake to start sanding without sandpaper on it and the hook & loop was destroyed. And for a hobbyist brand, that sander was a darn fine one and lasted me longer than any of the pro brands. It lasted 18 years, while the others never lasted longer then maybe 10. Only Festool might challenge that, but I don't know yet as I have my longest owned Festool, the RO150, for only 12 years now. 

As for humidity, that has no influence on plastics. Higher temperature makes molecules move faster, and thus makes chemical reactions happen quicker, but I doubt a handful of degrees adds a lot in this case.
 

That 40 year old unit is very likely to use PSA paper and I'm sure a different type of pad composition.
But yeah, I have had older ones that never experienced his degradation either, but again old. They were not a soft/flexy as the newer ones.

Ya you're correct it does use PSA paper, also the pad is a harder durometer and it's thinner so there's less to deteriorate.