Apparatus and method for internally sealing and sculpturing an elastic membrane expandable container is provided. One end of a generally hollow tubular insert extends into the container and stretches the elastic membrane of the container from the inside so that such end is sealed by the elastic force of the membrane. Another end of the insert extends out of the container with the container sealed therearound. The container may be pressurized by forcing materials such as fluids into the insert outward end and through the hollow insert so as to cause the elastic membrane to unseat from the sealed end thereof, thereby inflating the membrane. Once the pressure source is removed from the insert outward end, the elastic force of the membrane will cause it to contract and reseat against the tubular insert, thereby resealing it. Selection of the shape of the hollow tubular insert can in effect internally sculpture the container in a desired manner, while the hollowness of the insert in combination with its exposed outward end further provides access to the interior of the inflated container without breaking the seal thereof. Various other objects such as activated chemical lights or temperature regulation devices may thereby be selectively introduced to the container interior.