To describe lag time of Time-Controlled Explosion System (TES), the system's water absorption kinetics was investigated. Study of water absorption in TES with EC membrane revealed the following relations : (i) the square of water-uptake linearly increased with time in accordance with the Washburn equation, (ii) the water permeation rate correlated with the reciprocal of membrane thickness, (iii) the amount of water-uptake necessary for membrane destruction was directly proportional to the thickness of the membrane. These results suggest that lag time of TES is regulated by the function of membrane thickness. Indeed, the observed lag time was confirmed to fit with the curve expected by the above relations. When talc was included in the EC membrane in an equal weight ratio as a membrane-filler, lag time related directly to the membrane thickness. Compared with TES consisting of EC membrane only, the membrane was destroyed by a smaller amount of uptaken water owing to the weakening of membrane strength by the talc addition.