These are notorious for leaking. Shame as it's a great kettle. I had mine for less than a year before it started leaking, bit it had been in storage a while beige using so Bosch wouldn't help with warranty. You can take them apart to fix, but it's a bit of a faff.
Unfortunately out of stock now
Mine is plastic walled, with a steel circular sole-plate at the bottom.
I don't have one but from an Amazon review : the inside is plastic. One gets the impression that it's steel
Brilliant kettles, love the temperature selection. Had one now for about 4 years after a friend recommended one. Still going strong and no leaks