G-Floor is completely waterproof and will keep any moisture from penetrating through the product. However, if moisture exists in the concrete subfloor or underneath installed flooring, it will not be able to evaporate if trapped under the flooring. It is also possible for moisture to migrate under the flooring from around the edges if not fully glued down. The product cannot control moisture or debris from entering from around the edges or the underside of the flooring. Some possible solutions would be to have your concrete floor sealed before installing the G-Floor flooring mat and/or moving the mat periodically to allow the area underneath to dry, especially in areas of high humidity.