From Warre's 'Beekeeping for All', 12th Ed.:
The most healthy walls are those of the old skeps, in straw or osier, covered with daub. These walls are warm in winter, cool in summer and permeable at all times. They do not keep the humidity in. They attenuate variations in
temperature. In practice, because we need the regularity of a square form, we give preference to wood. Wood requires less monitoring and maintenance. As insects often hide in the straw, rodents attack more readily.
Wood is more resistant to insects, rodents and bad weather. A coat of white oil-based paint can, moreover, be quickly given, without driving the bees out.
We thus settle for wooden walls of 24 mm thick. A thickness of 20 mm is sufficient. A thickness 24 mm is preferable only from the point of view of strength. There is less play in the wood at this thickness.
Furthermore, in such hives, the bees go out sooner in the mornings because they sense more readily the ambient temperature.
Thicker walls increase the weight of the hive and its capital cost.
Double walls have the same disadvantage. In addition it is almost impossible to retain the enclosed air that should be an insulator and thus useful.
The insulating materials that can be placed between two boards are often expensive; they sometimes absorb moisture and cease to be insulators.
Furthermore, the insulating walls do not achieve their aim. In spring they delay the bees foraging sorties. In winter they do not economise on stores. On the contrary, the bees consume less when they are torpid with cold than when they are kept active.
Certainly, if single-walled hives are more susceptible to the ambient temperature by day, they are equally susceptible to the cold at night. But at night, the presence of the bees compensates for the lack of warmth.
And let us not forget that comfort weakens the stock, that striving, as Pourrat said, is the condition of life, adversity its climate.