Which is the inductor-core used in the high performance L-C filter?

Hi Nikhildascel
Can you tell me a bit more explanations about what you need exactly , please ?
Best Wishes
Goldsmith

The answer is: Air.
And the resonator type for most of the high-performance LC filters is Helical.

why is it so vfone why can't we use material having more insulative properties as a core to improve the resonance like Ceramic and stuff

I agree for frequencies above e.g. 10 MHz. But nothing's been said about frequency range in the original post.