Well well, I've said it myself. It's the product. (Backing specifically) My experience was that width expanded, never length. The width backing has like a coated(latex and fillers) strands, the length are flat and wider. This is just me, I will not warranty from wrinkles, I power stretch, I feel the carpet and tighten it to a limit I know tackstrip will support and backing will allow me to stretch it. I don't install much carpet anymore, moved on to other problems!

It's some what the construction of the backing.The weft cords are the culprit as they are the heavier cord. Basically all the backing is plastic that doesn't like give and take to start with and then you introduce a pad that is not the right density and to soft or thick it all adds to the mix. I attended a seminar on backing once and it was stated that action back has that little flaw lets say that it will require a restretch in time. Actually I got one in my own home right now. 10 x 12 bedroom. This room get a tremendous amount of traffic as it is also my laundry room, and it is in the traffic lane to the appliances. Been down about 6 years now. Daris

I have seen more in manufactured homes here. Moisture from below is presumably the culprit.