Hi Sayantan, you can have either good thermal resistivity or good thermal conductivity, but not both. For thermal insulation purposes, you need high thermal resisitivity, with low thermal conductivity, so it would be better to avoid nanofluids for this application because nanofluids generally have high thermal conductivity.

If you need the fluid to transfer heat before entering the insulated area, then you could use a nanofluid for the heat transfer, but increase the resistivity of the tube/conduit material by changing to a high thermal resistance material of the insulation area. Good luck

As Sylvio mentioned, nanofluids are usually used for their enhanced thermal conductivity. But I suppose if you synthesize a new nanofluid containing nanoparticles with a k value much less than that of the base fluid perhaps you can decrease its thermal conductivity. Or maybe not!

In general metals are good conductors of heat. extensive work was reported with regard to enhancement of heat transfer by improving the thermal conductivity of water by dispersing nano metal particles. if it possible to manufacture, disperse them with proper mixing and one can try it. it is a prediction only. you may try for it.

there is no material which posses "great thermal resistivity and very good thermal conductivity".

i think your question might be "electrically resistive and thermally conductive" or thermally resistive and electrically conductive"

but most of the metals are good thermal as well as electrically conductive in nature