Twist off the coolant base of these BPA-free cups and freeze them upside down. We froze one base and left one unfrozen, then filled both cups with 41-degree water. In 45 minutes, the frozen cup held the water to 44 degrees, still nicely cool. The unfrozen cup was at 50 — a marginal temp for soda or beer should that be your fare. In an hour the frozen cup held to 53 degrees, while the unfrozen cup climbed to a nasty 58. We like the durable construction and bright colors but found them a little too narrow to be secure in cup holders while traversing bumpy waters. Still a cool buy at six cups for $16.99; chillytwist.com
