Why will a cup of coffee with lot froth on the top keep hot for longer thn one without froth?

A cup of coffee with a lot of froth on top won't actually keep hot for longer than one without froth. Here's why:

* Froth is primarily air. While froth can create a temporary insulating layer, it's mostly air, which is a poor insulator. Air allows heat to escape more easily than a denser material.

* Froth cools down quickly. The air bubbles in froth are very unstable. They pop and dissipate quickly, leaving behind a thin layer of liquid that doesn't offer much insulation.

What actually helps coffee stay hot:

* A lid: A lid traps heat and prevents it from escaping.

* A ceramic mug: Ceramic is a better insulator than glass or thin plastic.

* A double-walled mug: Double-walled mugs have a vacuum between the walls, which prevents heat transfer.

* Insulated sleeve: A sleeve adds an extra layer of insulation to help keep the coffee warm.

So, while froth might make your coffee look appealing, it won't do much to keep it hot for longer.