Water Activated flood bags (Sandless Sandbags). Bags grow to 12" x 24" x 3.5" high. No need for sand or labor, filling sandbags. Absorbs 4 gallons of water and grows to full size 3.5" high in 10 minutes. Contains a super absorbent powder that swells and gels water. Swelled bags contain, control, and divert flood water. Stack multiple bags in brick formation to increase wall height. Safe, non-hazardous, non-toxic, environmentally friendly and decomposes over time. Not for use with salt water- a chemical reaction causes deflation. 6/pkg.