Descriptions: This tire valves stem cap is designed with luminous material.When installing for the first time, please shine a light or sunlight on the tire valve for 30-60 seconds to make it work better at night.A wonderful and surprise gift to your friends. Specifications: Material: Silicone Color: Green, Blue(optional) Size: 0.63 X 0.48 X 0.31 inch Package Included: 8 x Tire Valve Caps Notes: 1. Please allow 0.1-0.4 inch error due to manual measurement. Thanks for your understanding. 2. Monitors are not calibrated same, item color displayed in photos may be showing slightly different from real object. Question:Will it glow tonight? Answer: Yes, please illuminate the tire valve with light or sunlight for 10-15 seconds, the effect will be brighter at night. (Glowing provided you let it absorb enough sunlight during the day) Q:Is this tire cover silicone? A: This tire cover is natural rubber & covered by outer layer of silicone. Q:Can the tire valve cover be used on bicycle or motorcycle tires? A: We can confirm that it meets all US standard bikes, motorcycles, cars, trucks, SUVs on the market.