Core-shell dry water (DW) has attracted significant attention as a promising candidate for future fire extinguishing agents, owing to its high water content, powdery structure and ease of handling. However, the lack of detailed information regarding the characteristics of DW has considerably hindered efforts to improve its fire extinguishing performance. This study is the first attempt to elucidate the origin of the effects of particle size of DW on fire extinguishment. Pristine DW was fractionated into three different particle sizes via careful sieving. Through systematic analyses, it could be determined that smaller DW could be vaporized at lower temperatures, thereby facilitating good cooling and smoldering of flames. However, small DW cannot sufficiently penetrate flames, which makes it difficult to reach the burning surface. However, medium-sized DW exhibited a balance in its cooling, smoldering, and penetration effects. Thus, it achieved better performance in fire extinguishment when compared to small- and large-sized DWs. It was also demonstrated that the fire extinguishing capability of medium-sized DW can be significantly enhanced by adding NaHCO3 in the water core of the DW.