Hydrotite Hydrophilic Waterstop consists of a unique combination of expanding hydrophilic materials and non-expanding chloroprene rubber, co-extruded together to form a single strip. The co-extruded design means that the expansion is directed across the joint for maximum sealing performance. This expansion creates an effective compression seal within the joint, preventing the egress of water through it. Upon expansion, Hydrotite turns from a dark blue colour to a light blue colour, so that a visual inspection of the Hydrotite can be made and so the contractor can see if the Hydrotite has pre-expanded.