18k gold plated on stainless steel. Color and shine is guaranteed for every day wearing for at least two years with daily normal wearing. If you wear it on and off then it lasts longer than two years. 

They are nickel and lead free/hypoallergenic so they don't give you itching or scratching when you wear it. 

The chain size for men is available in 20” and 24”.

The chain size for women is available in 16” and 18”