Disposable diapers haven't been around long enough to allow time for researchers or other people to find out exactly how long the disposable diapers will take to decompose.
However it's said that disposable diapers will take around 500 years to fully decompose if they ever do decompose.
Disposable diapers contain some plastic that may never decompose.
I read online somewhere that someone was digging up the ground in their backyard in the country and found some old Pampers disposable diapers from 30 years ago that were still very much intact without much decomposing.
The person assumed they were 30 year old Pampers because of the full plastic backing of the diaper which they were back in 1980's.
I do know that in 1988 Pampers and other disposable diapers were fully made of plastic and thicker than they are today.
They had the plastic tapes instead of Velcro.
The newer diapers may decompose in less time but still they may not for many years.