Even better? Some of the most popular Hydro Flask cups are on sale right now at Amazon starting at just $18. Related: Declutter Your Kitchen with These Clever Kitchen Storage Finds from Wayfair ...

We wanted to find out which cup keeps drinks colder longer. For our experiment, we added two more popular brands: A 40-ounce Hydro Flask for about $40, and a 35-ounce Yeti for around $42.