Brompton seatposts are available in three types, and in steel or titanium:

The standard-length post makes for the smallest folded size, and is suitable for people up to about 5’10” tall.

The extended post is 6cms longer, good for people up to about 6’2” tall - though the saddle is also 6cms higher when the bike is folded.

The telescopic post works in two stages, so it will suit the very tall - over 7’ with no problems. It’s slightly longer than the standard post due to the size of the second clamp, so the saddle is about 2cms higher when folded.

Any of these seatposts is available in titanium instead of steel, to save 250-300g. The titanium posts have a tough blue finish.