I received my first Chilly bottle recently and there was some slight markings on the inside of the neck of the bottle. I emailed a photo of this to customer services to ask what it was, and without prompt they simply said they would send a replacement bottle and not to worry about returning the one with the marks! The 'faulty' one is still perfectly usable and now I can have one in my car and one in my bag. Incidentally - I left one in my car on a rare blazing hot day in the UK when the temp was around 30 degrees. When I returned early afternoon I was stunned that the water was still very chilly! I love this product and have recommended them to my family & friends!