Hartwick Clearcup Double-Wall Glass

The Clearcup is the budget route into double-wall glass: a single 300 ml borosilicate cup with a sealed insulating air gap between its walls. Borosilicate handles sudden temperature swings that would crack ordinary soda-lime glass, so you can pour just-off-boil water directly in. The air gap slows heat loss and keeps the outer wall comfortable to grip, no handle needed, and the clear walls show off the layers in a milk drink or the color of a light roast. At 300 ml it fits a standard pour-over or a large flat-white-style drink. Top-rack dishwasher-safe; avoid abrasive scrubbers, which haze the glass over time. Not as ornate as pricier double-walls, but the physics are identical, and the price means you can buy two.