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Top 3 Reasons Why People Buy This:

1. Able to reduce or increase size anytime & anywhere
2. Built with high-quality food grade silicon

3. Very unconventional and interesting design which makes for a great gift!
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Technical Specifications:

Material: Food-Grade Silicon, BPA-free plastic, Stainless Steel

Size: 200ml~400ml
200ml~500ml

Thanks for looking through! 

If you have any questions, feel free to ask!