In a log cabin there's no actual insulation in the home like a regular stick built home with be with drywall.
The logs themselves are the insulation between the interior and exterior of the the log home and even though there's no traditional insulation my log home or log cabin is very warm in the winter and cool in the summertime.
The logs are a great natural insulator and actually I find my log cabin to be warmer in the winter than a traditional house would be.
The R-value for wood logs ranges between 1.41 per inch (2.54 cm) for most softwoods and 0.71 for most hardwoods.
The log cabin I live in actually holds in the heat much better than a traditional home does.