All materials conduct heat, some more than others. Materials that are poor conductors of heat are good insulators.
Insulating materials have a high level of resistance to conduct heat.
This resistance is measured in R-value. The higher the R-value, the better it is as insulation. During the course of building the house, I have received letters from some asking if I have strayed a bit off of the path of building a natural house. I do make an effort to use natural products where it makes sense. There are always tradeoffs to consider.