You want to get a travel tumbler that has a stainless steel interior. While plastic ones can work well for a bit, they will break down over time and begin leaking gas through the wall and into your drink. 18/8 304 food-grade stainless steel is your best bet as they are corrosion resistant, unbreakable, and keep drinks at their ideal temperature due to the bottle’s double-walled vacuum-sealed insulation.