Insulated French presses

A standard glass French press loses heat fast: thin borosilicate, a large surface area and a lid that is mostly a hole. Insulated versions put a vacuum or an air gap between the coffee and the room, and the practical result is that the second cup is still hot twenty minutes later.

Heat retention and brewing temperature are different problems

Insulation does not make the brew hotter, it makes it stay where it started. It also means the brew itself runs slightly warmer for the four minutes it steeps, which very slightly increases extraction. If your press has been giving you weak coffee, that is a grind or ratio problem rather than a heat one: how to use a French press properly covers the recipe.

The trade you make for it

A vacuum-walled steel press is opaque, so you cannot see the bloom, the plunge or how much is left. It is also heavier, more expensive, and cannot be put in the dishwasher in the way plain glass can. And a dented vacuum wall has lost its vacuum permanently, where a broken glass beaker is a cheap replaceable part on most models.

It does not stop over-extraction

This is the point most people miss. Coffee left sitting on the grounds keeps extracting whether the press is insulated or not, and keeping it hot makes that happen faster. If you are brewing more than one cup, decant into a mug or a carafe when the timer goes. An insulated press is for keeping DECANTED coffee hot or for drinking through quickly, not for parking coffee on its grounds for half an hour.

Where it earns its money

Offices, cold kitchens, slow mornings, and anyone who brews a full press for two people. If you drink one cup immediately, plain glass does the same job for less and lets you see what is happening.