SUMC Chain, 9 speed EL 9Extra light
 
SUMC is colour coated making it abrasion and corrosion resistant. The chain last much longer with the coating in addition to the refreshing look.
The outer plate design allow you to shift smoothly between gears for better power transfer. 
 
A good choice for Brompton bicycles standard 6 speed gear. i.e. 3 speed Sturmey Archer internal hub gear with 2 speed external gear drive.
 
This mid-level EL-series chain are semi-hollow for lighter weight and enhance reliability.