The reason some London Tube stations have extra doors – human hair (mylondon.news)

Other systems have half-height platform screen doors, and some lines that run outdoors use them, so separating the in-tunnel airflow and the station airflow (filled with hair apparently) is probably not the only engineering concern.

I did some more reading and found these rope-type barriers in Japan: https://www.youtube.com/watch?v=_TFXGJe8s-E

Yeah, I'm a bit dubious about this being the prime reason for the platform doors too, but fluffers are a real thing - see https://www.wikiwand.com/en/Fluffer_(London_Underground)

The Wikipedia article on the [Jubilee line](https://en.wikipedia.org/wiki/Jubilee_Line_Extension) doesn't mention hair specifically, but does mention they're to improve airflow, prevent jumping or failing people, prevent litter and dirt circulation. I always imagined it was in preparation for the move to automated lines much like the [Docklands Light Railway](https://en.wikipedia.org/wiki/Docklands_Light_Railway) which demonstrated feasibility in 1987 (11 years before Jubilee).