my sister has a log home; full logs tend to work pretty well as insulation; typically you get ~4 inches of solid wood between inside and out, takes a bit of time and work for thermal change to get through (one of the directives for people lost in a wildfire used to be to get into a log cabin and shelter there; the walls take a good while to ignite). the bigger issue with them tends to be that all the cracks and crevices make for an excellent hiding ground for spiders (and scorpions if you're in the right area)