All three Baggies were outstanding for their draw at Aston Villa on Sunday.
Foster said: "Jonas and Gareth have been that way since the middle of last season. They are absolute warriors. You know they are going to block everything, head everything, kick everything.
"They took some serious knocks against Villa. They have got bumps and bruises all over, but they will always be in there fighting for you and it's nice to have two people like that in front of you.
"I don't think there are many better centre-back pairings in the Premier League. They play week in and week out I don't think they've missed a game for a good long time.
"You take all those things into account and I'd much rather be playing with those two than the majority of defensive pairings."