Parenchyma cells and fibers are the two dominant types of cells in the bamboo culm. Their mechanical and biological functions in bamboo differ substantially, derived from their cell wall structures and chemical compositions. The objective of this work was to comparatively study the hygroscopicity and the thermal degradation of bamboo fibers and parenchyma cells in order to better understand how to optimize heat treatment of bamboo. FTIR spectroscopy showed that parenchyma cells had a higher hemicellulose content and higher S/G lignin ratio than bamboo fibers based on the spectral changes at 1602 cm−1 with respect to 1505 cm−1. Upon heat treatment, spectral changes related to esterification reactions and loss of hydroxyl groups were observed. The heat treatment reduced hygroscopicity of parenchyma cells more than for bamboo fibers due to their lower thermal stability attributed to the higher hemicellulose content and less compact cell wall structure. Although heat treatment at 180 °C could improve the thermal stability of bamboo, mild heat treatments at 140 °C and 160 °C were found to be adequate to facilitate the degradation of bamboo. © 2021, The Author(s)