Handmade, please allow almost no deviation. The interior is made of selected sea sand, the interior of glass and the exterior of strong plastic with double protection. A good timer that kids can use to have a clear idea of cooking timing and time. An elegant gift for family and friends. Since the hourglass does not exactly match the clock, please allow 10% error. It has good sealing, but looks like it sometimes penetrates. If the sand gets stuck, the timer just needs to stay in the sun for a while. Since the hourglass does not match the clock exactly, please allow 10% error. It has good waterproof , but air sometimes gets into it. If the sand gets stuck, the timer just needs to stay in the sun for a while.