Super heavy duty and it’s held up very nicely. I think that the bag has no issues in holding heat nor allowing you to feel the heat through the bag. Great product for a great price. Plus the design is cute.Help reduce my arthritis pain during this cold weatherIt is a sturdy, well made thick bottle BUT it doesn't transmit real heat, only warmth. I should have returned it. Fairly useless for my needs.Sorry I can’t read English很好?It’s thick & can handle boiling water. I love itOrdered one and it leaked, so returned it and the 2nd one leaked.that thing is leakingCaution! This hot water bottle has sprung a leak in one of the seams.