Penders, who has signed from Belgian side Genk, has become the latest addition of another busy transfer window at Stamford Bridge as they add the keeper to a squad of over 40 players.
The keeper put pen to paper on a contract to 2032 and will spend this season back at Belgian side Genk as it is unlikely he would earn minutes on the pitch for the Blues.
Filip Jorgensen signed from Villarreal earlier in the summer and now with Penders the club has six options to choose from if any injuries crop up during the season.
Penders made his senior debut in July, becoming the third-youngest goalkeeper to play in the Belgian Pro League.
The 6ft 7in Belgium Under-19 player is a hot talent which is exactly what Chelsea have been signing this summer in what has been a hectic window which takes the club's spending above £150m.