Interesting! I checked out what the RNLI had to say at https://rnli.org/safety/lifejackets and that page only mentions lifejackets along with gas.
However, if you "Download our lifejackets and buoyancy aids guide as a PDF (3.48MB)" at https://rnli.org/-/media/rnli/downloads/1983319_choose_it_we... you'll read "Children’s lifejackets may rely on foam, air and foam, or CO2 only to provide buoyancy" and "Air and foam or CO2 lifejackets meet the requirements of a level 150 lifejacket and are suitable for offshore use. Normally, foam lifejackets provide level 100 buoyancy
and are suitable for inshore use."
A further search of the RNLI site finds https://rnli.org/magazine/magazine-featured-list/2018/june/t... with "The foam-based Beaufort lifejacket [of the 1970s] upped the buoyancy level, allowing a crew member to also support the person being rescued." but by the 1990s "The bulkier gear of all-weather lifeboat crews meant they needed a more compact lifejacket, which inflated automatically on hitting the water using a built-in gas canister."
Since I learned my small watercraft skills in the warm waters of Florida, instead of chilly UK, I can see how that would make a difference.
In boating a life jacket does not need to be inflatable. https://uscgboating.org/recreational-boaters/life-jacket-wea... says:
> There are four basic design types: Inherent, Inflatable, Hybrid, and Special Purpose.
> There are two main classes of PFDs.
> * Those which provide face up in-water support to the user regardless of physical conditions (lifejackets).
> * Those which require the user to make swimming and other postural movements to position the user with the face out of the water (buoyancy aid).
It mentions both "Foam filled lifejackets" and "Inflatable lifejackets".