I think chubby is polite enough :) or overweight ?

Honestly, there's no polite way to say fat. there are a number of ways to say it without being so crude. chubby, overweight, big, heavy, well built, big boned.. Personally if you said any of that to me, I'd get a little offended. It's never polite to discuss someone's weight since many people are self conscious about their weight and already know they are too fat, or too skinny. I have a friend who says she's big boned. and another doesnt mind being called chubby. it all depends really. if you have to, I'd say chubby. or just tell them they look cute and fluffy.

We are using plump and "big boned" in the US!- A statement of denial.

Chubby----胖乎乎的 Overweight ------ 超重

There's no polite way to say fat,especially if you are describing woman ;) But more neutral word is - "chubby"