No consumer health risk from bisphenol A exposure, European Food Safety Authority, January 21, 2015 Button-operated lids are more efficient to use than twist-and-pour stoppers – we found the button-operated lids to be more secure than the twist-and-pour stoppers. Jenna Bilbrey, BPA-Free Plastic Containers May Be Just as Hazardous, Scientific American, August 11, 2014 We hand-washed each flask with hot soapy water and let them air dry overnight, then ranked them on smell.

Stainless steel is also cost effective and helps to prevent unwanted odours seeping into your delicious coffee drink. We dropped each flask five times from 90cm to mimic a dropped flask. Those with large dents that inhibited function or ability were rated low. Pay attention to details like leak-proof seals, insulation technology, comfortable grips, and easy-to-use lids. Jocelyn Ivanov, MIT, Drinking fountains: the past and future of free public water in the United States, September 29, 2015 None of the flasks leaked from the main body – however, some flasks can't be filled to their stated capacity without liquid coming out when you screw on the lid.Johanna R. Rochester, Ashley L. Bolden, Bisphenol S and F: A Systematic Review and Comparison of the Hormonal Activity of Bisphenol A Substitutes, Environmental Health Perspectives, July 1, 2015 This does depend on factors like the flask's insulation technology, the size of the flask, the starting temperature of your coffee, and how frequently you open the flask. You’ll get the best thermal performance by putting your Hydro Flask in a place that’s cool when it’s filled with something cold or a place that’s warm when it’s got something hot inside. In the heat of summer, your ice water will last a lot longer if the bottle is in the shade instead of direct sunlight. Likewise, don’t expect your coffee to stay hot for hours if you leave your travel mug on a snow-covered sidewalk as you shovel the driveway. A little common sense goes a long way in reducing the rate at which your Hydro Flask will reach temperature equilibrium with its surroundings. How We Tested Flasks are more 'smell prone' than 'stain prone' – none of the flasks we tested had any staining after cleaning, but some retained a faint coffee smell. Hydro Flask makes beautifully designed gear from drinking bottles and coffee cups to Soft Coolers and the Outdoor Kitchen dining collection. Hydro Flask’s bold and bright range of products and interchangeable accessories are perfect for commuting, camping, climbing - or whatever outdoor activity floats your boat.

Textured coatings are useful – it’s a nice touch to have a handle on a drinks flask but generally, for a one-litre flask, it’s more useful to have a textured coating that provides grip. To find the best Hydro Flasks, we compared six bottles of various shapes and sizes and seven styles of lids, considering the cost, weight, usability, and insulating performance of each. We assessed insulation as follows: Since the American manufacturer, Thermos, came to fame, the term has become slang for vacuum-insulated flasks. Although the terms are largely interchangeable, the original scientific phrasing is 'vacuum flask'.Jon Hamilton, Beyond BPA: Court Battle Reveals A Shift In Debate Over Plastic Safety, NPR, February 16, 2015

All of which we have covered in our list of recommendations. Will coffee stay hot in a Hydro Flask?

Plus, you don’t have to worry about staining your newly bought flask. What is a good quality thermos?