The Rambler® 5 Oz Cup Cap. Save some space by transforming your Rambler® Bottles with our heat-locking, two-in-one companion — the Cup Cap. Not only is it compatible with every Rambler Bottle, but it also offers twice the functionality. As an insulated cap, it helps keep your coffee, tea, or even whiskey at the perfect temperature. And when you twist it off, you’ve got a double-wall vacuum insulated cup.