I left this filled with water overnight while horizontal and it didn't leak. Have also tried shaking it upside down and didn't see any leaks. Caveat is that I haven't tried to microwave or freeze it yet, which could maybe lead to seal deformation later, but time will tell. I wonder why they didn't just print the "eyes" of the bird on the bottle itself? The included "sock" has the eyes, but because the threads weren't "finished" neatly in the back, you can kind of see them, through the white fibres. Like a bird with dripping makeup on. Kind of funnier because of this. Inside out, the sock looks a bit clown-ish. I wouldn't feel confident putting this sock in the machine wash because I'd guess the eye/beak fibres would all fall out.

2nd one I bought for myself. super cute.

Super cute design. Nice material!

Very cute little product.....keeps warm for a long time!

Works well…no leaks…great compact size

comfortable