A: “Woah, woah, I’ve put on a little weight?”
B: “No, not weight… y’know, more like insulation.”
In this conversation, what does “insulation” mean?
What is B trying to say?
Thanks. 
Fat. B is trying to minimize the negativity of her gaining weight by suggesting that it serves the positive purpose of insulating her body against the outside temperatures.
Oh, OK. Thank you.
So this way to minimize the negativity would only work in winter, or very cold day, right?
Pooh, it can be said all year round. It’s humorous. It just offers an excuse for the weight gain.
OK, so it’s just an expression. I see.