Does a vacuum tumbler really stop condensation?

Yes. The vacuum between the two walls of the tumbler prevents the cold from reaching the outer surface, which means no condensation forms. A good vacuum tumbler is dry to the touch even with ice in it.

Can I use a regular coaster instead of a tray?

On a flat surface, yes. On a couch armrest, no. Coasters are too small, too rigid, and too easy to slide off when the cushion shifts. A tray with a raised lip is the right shape for the job.

What is the best iced coffee tumbler for the couch?

Any well-reviewed double-walled vacuum tumbler in the 16 to 20 ounce range with a handle and a tight lid will do. Brand matters less than the basic specs.

Summer iced coffee on the couch without the panic

The three things that go wrong

The summer iced coffee on the couch has three failure modes, and the rest of the panic is just one of them happening. Solve all three and the ritual goes from stressful to obvious.

Condensation pools and runs onto the cushion.
Cushion shifts and the cup tips.
Reaching for the cup breaks the slouch and spills.

How to solve all three with two objects

First object: a vacuum-insulated tumbler with a wide handle and a tight lid. The vacuum kills the condensation. The handle gives a one-handed grip. The lid means a tip does not become a spill.

Second object: a tray or caddy that drapes over the armrest with a real raised lip. The tray catches what the tumbler does not. The lip means the tumbler does not slide off when the cushion shifts.

Why a regular glass is the wrong choice

A regular glass on a couch armrest in July is going to leave a ring on a cushion within a week. The glass sweats faster than felt absorbs, and felt is not on the couch anyway.

Glasses are right for dining tables, not couches. Save the glassware for when you sit at the table.

Vacuum tumbler buying notes

Look for double-walled, not single-walled. Single-walled sweats almost as much as glass.
Get one with a handle. A handle keeps the cold from numbing your fingers and gives a stable grip.
Avoid straws with paint or printing. Straws lose their finish faster than the cup does.
Match the tumbler to the cup well in your caddy. A 20-ounce wide-mouth fits most caddies. A 30-ounce does not.

The morning version of this

Some people will argue that hot coffee in the morning and iced coffee in the afternoon is the only correct order. Others will switch to iced for the entire summer. Both are fine. The mechanics are the same: a heat-stable surface for the cup, a tumbler that does not sweat, and a tray that catches what the tumbler does not.

After three summers of testing every cup-on-couch setup we could find, the silicone tray plus vacuum tumbler is the only combination that does not require any clean-up at the end of the night. Everything else has tradeoffs.