Ok, as you know, I have some thousands of hours of working in security. Besides nylon 66 for hide guns. you also have a specific cement grease ( grease is an oil substance, very effective on hiding purpose, and cement very dense, besides the thermal aspect for gamma ray detection) , very affordable and effective

30g High Performance NEW Heat Sink Compound Grease Paste Affordable GD900 Neu~ | eBay

GD900 thermal paste. 1 GD900 thermal paste. High thermal conductivity, efficient insulation, high temperature, low oil non-corrosive. Thermal conductivity: 4.8 W / M-K.…

EBAY.COM

https://www.ebay.com/itm/30g-High-Performance-NEW-Heat-Sink-Compound-Grease-Paste-Affordable-GD900-Neu/123001614107?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649