Paper nests of wasps and hornets were investigated by means of differential scanning calorimetry (DSC), thermogravimetry (TG) in combination with mass spectrometry (MS), combustion calorimetry (CC) and some other biophysical techniques. Nests are constructed of thin paper layers (0.1 mm thick, area density 76.5 g m(-2)) formed of rotten wood and strengthened with saliva as adhesive. The nest material is water repellent with extremely low water content (about 3%). Paper nests establish a microclimate for the insect colony due to the good thermal insulation (heat conductivity 0.08-0.20 W (degrees C m)(-1) comparable to that of some bird nests or of good natural and technical insulators. DSC and TG thermograms show that cellulose is the main component in the wasp paper offering high tensile strength against deformation and a low specific weight for light construction and easy transport.