What is an electric kettle made of?

Nichrome wire in a magnesium-oxide-filled steel or aluminium sheath

Nichrome has high resistivity and doesn't oxidise away when it glows. The magnesium oxide insulates electrically while still conducting heat outward.

Stainless steel (usually 304), borosilicate glass, or polypropylene

304 stainless resists the chloride corrosion that tap water causes. Borosilicate survives repeated thermal shock. Polypropylene is cheapest and tolerates boiling, but it is the surface most associated with taste complaints.

Bimetallic strip — two bonded metals with different expansion rates

Steam is channelled onto the strip; the metals expand unequally, the strip bends and trips the switch. It is a purely mechanical sensor, which is why it works with no electronics at all.

Moulded polypropylene or silicone tube

It routes steam from the spout area down to the thermostat. Blocking it — or leaving the lid open — is why a kettle sometimes fails to switch off.

Polypropylene housing with a brass or steel 360° contact ring

The ring lets the kettle be placed in any orientation. It's a wear point: arcing at the contacts is a common late-life failure.

Polypropylene, sometimes over a steel insert

Polypropylene's low thermal conductivity keeps the handle cool. On steel kettles the join between hot body and cool handle is a deliberate thermal break.