Jennifer Garner thinks husband Ben Affleck has "wonder sperm".

The 40-year-old actress shares two daughters and a son with her actor-and-director spouse.

Jennifer is not keen on expanding their family any further, but since Ben is so virile she will not discount the possibility of a future pregnancy.

"No, I definitely I plan to be done," she revealed on Thursday's episode of The Ellen DeGeneres Show.

"But my husband is kind of a wonder sperm kind of guy."

Jennifer gave birth to baby boy Samuel in February.

While he may be too young to partake in playtime with older sisters Seraphina and Violet, Jennifer reveals that Ben acts as a good stand-in for the girls.

"You know his girls are so into him," she gushed.

"He's all about He kind of excels at playing baby doll... Yeah, he can do it without using any energy at all."

Jennifer was also full of compliments for Hollywood parents Brad Pitt and Angelina Jolie.

She admires their ability to look after six children.

"Oh man Talk to Brad and Angie they seem to have it together!" Jennifer said.