Is helium a good insulator why?

Answer 1

Not bad, but not great.

It's a gas, so it doesn't conduct electricity unless ionized,

it's a gas, so heat conduction is poor except for convection, and it's low molecular weight would result in very high flows to move heat energy,

Answer 2

Helium is not a good insulator because it has very low density, which means its atoms are far apart and it does not trap heat well. Insulators are materials that can slow down the transfer of heat, and gases like helium are not as effective in this regard compared to solid materials like glass or rubber.