This chiller has truly simplified - and given me great confidence - going back to work while breastfeeding. I end up filling the inner piece with water and freezing overnight. Although I don't pump enough throughout the day to even touch the iced inner piece, it STILL keeps my milk cold for an entire work day (sometimes up to 9 hours/day). Just a quick swirl of milk so it at least touches the ice, and it's good! Back in October I was traveling and ended up checking my *full* chiller in my luggage. When I arrived home after 20 hours of traveling, the milk was ice cold and the inner piece was still frosty! So impressive - I highly recommend this necessary tool for any breastfeeding mom.