This custom dry-top stopper with refillable inner chamber housing indicating desiccant, fits round-bottom and Erlenmeyer flasks with 24/40 necks. It offers you temporary or long-term storage in an anhydrous environment without requiring a desiccator. Composed of FEP (fluorinated ethylene propylene) plastic, the translucent stopper allows you to easily monitor color changes (from blue to pink) for constant visual assurance of active indicating desiccant. A vapor-permeable and chemically resistant membrane ensures the desiccant will never contaminate your sample.