This study reports on the unique water vapor adsorption properties of biomass-derived starch particles (SPs). SPs offer an alternative desiccant for air-to-air energy exchangers in heating, ventilation, and air conditioning systems because of their remarkable adsorption-desorption performance. SP15 has a particle diameter (d p) of 15 μm with a surface area (SA) of 2.89 m2/g and a pore width (P w) of 80 Å. Microporous starch particles (SP15) were compared with high amylose starch (HAS15; SA = 0.56 m2/g, d p = 15 μm, P w = 46 Å) and silica gel (SG13; SA = 478 m2/g, d p = 13 μm, P w = 62 Å). Transient water vapor tests were performed using a customized small-scale energy exchanger coated with SP15, HAS15, and SG13. The water swelling (%) for SP15 was ca. 2 orders of magnitude greater with markedly higher (ca. three- and six-fold) water vapor uptake compared to HAS15 and SG13, respectively. At similar desiccant coating levels on the energy exchanger, the latent effectiveness of the SP15 system was much improved (4-31%) over the HAS15 and SG13 systems at controlled operating conditions. SP15 is a unique desiccant material with high affinity for water vapor and superior adsorption properties where ca. 98% regeneration was achieved under mild conditions. Therefore, SPs display unique adsorption-desorption properties, herein referred to as the "Goldilocks effect". This contribution reports on the utility of SPs as promising desiccant coatings in air-to-air energy exchangers for ventilation systems or as advanced materials for potential water/energy harvesting applications.