[Robin Ray]

I had a really bad rippler this week. Wool pile with a synthetic backing. I normally advise in the rare cases it happens that it will relax out again, but in this case it was so drastic I thought it would never happen. The customer is due to have a heart bypass later this week so I scheduled to go in this morning to stretch it out so they had nothing to worry about. I arrived to find not a ripple or bump in sight ( I wish they had called me).
Anyway what causes ripplers? The only thing I can think of is that the wool fibers packed in to the synthetic backing expand with the moisture making the whole carpet larger as a result. I think in this case it was exacerbated by the fact I was also applying protector, ie more moisture. The carpet was almost touch dry when i left after the clean but I suppose the wool had sucked up moisture and was holding it like a sponge. Is that the reason or are there any other explanations?

[john martin]

it seems random and suprises you out of the blue like u said  ,  thankfully rare enough . Probably exacerbated by overwetting with the hydroforce or wand at times .

[Mike Halliday]

I’m not sure what it happens but i’ve noticed it tends to happens on Cheap to mid range carpets not really good quality ones.

It would be an interesting comparison to bonnet clean a carpet  then wet clean it to see if it’s the moisure that creates the problem. Or ask a company who only uses a dry clean method if they get ripplers

[AJB]

It's heat or humidity expansion of the latex in the backing. The origins of the problem
are too little tension on the carpet when fitting. Funnily enough I haven't seen one
for over 4 or 5 years. If it's fitted properly it relaxes, that's when dragging furniture
can catch and stretch it.
Worst I ever had happen to me was an 80 oz wool carpet that expanded by at least a
foot, looked like the sea.

[Robin Ray]

It's heat or humidity expansion of the latex in the backing. The origins of the problem
are too little tension on the carpet when fitting. Funnily enough I haven't seen one
for over 4 or 5 years. If it's fitted properly it relaxes, that's when dragging furniture
can catch and stretch it.
Worst I ever had happen to me was an 80 oz wool carpet that expanded by at least a
foot, looked like the sea.

Same here, It literally looked like the sea, but relaxed out with no visible problems all by itself. I have had to stretch carpets out, cutting off inches before cleaning in the past though as they were so badly fitted.