Double-walled glass
A borosilicate cup made as two skins with a sealed air gap between them. The air gap is a poor conductor, so the outer skin stays cool enough to hold while the tea inside stays hot longer than it would in a single-walled glass — the same principle as a vacuum flask, without the vacuum.
Identity
- Category
- Drinking vessel
- Also called
- insulated glass cup, floating glass, double wall tumbler
- Material
- Borosilicate glass, two skins with a sealed air cavity
- Typical capacity
- 80–400 ml
- Skill level
- Beginner
Porosity
Not porous. It contributes nothing of its own to the liquor, so it can be moved between teas freely and washed with detergent without consequence.
Where it comes from
Modern and international.
Named here rather than presented as generic equipment. The object belongs to a practice, and TeaHQ describes it from the outside.
If you do not own one
A single-walled glass and a coaster, or a mug with a handle. Double-walled glass is chosen for showing liquor colour while being holdable, which is a real if modest combination.
This one is not marked essential. The tea can be made without it.
Brewing methods it is used for
- Grandpa style — Leaf loose in a tall glass or flask, topped up with hot water through the day and drunk around the leaf. It is how an enormous proportion of tea is actually consumed in China, and it needs no equipment whatsoever.
- Mug infuser brewing — Loose leaf in a basket inside a mug — the most common way loose tea is actually made, and the method most often responsible for people concluding that loose leaf is not worth the trouble.
- Cold brew tea — Leaf steeped in cold water in the refrigerator for several hours. Low temperature extracts the sweet and savoury compounds readily and the bitter and astringent ones barely at all, producing a cup that is genuinely different rather than simply a chilled version of a hot one.
Tea types it suits
Care and maintenance
Hand wash. A dishwasher forces water through the tiny vent hole most of these have, and once liquid is inside the cavity it will not come out and clouds permanently. Do not put one in a freezer.
Other drinking vessels
Sources
This page is TeaHQ synthesis. No external source stands behind the description, the material or the account of how the object is cared for. Where the record names a tradition, that attribution is TeaHQ’s own reading of common practice rather than a citation.
TeaHQ names no maker, brand or shop and has nothing to sell. Nothing on this page should be read as advice to buy the object — the substitute note above exists because owning it is usually optional.