Abstract: This paper introduces the measurement principle, air chamber structure, and operating procedures of the rubber permeability testing standard GB/T 7755, and how to test automobile inner tubes according to this standard. It also compares this test method with current automobile inner tube permeability testing methods. Keywords: Standard; Permeability; Automobile inner tube; Testing; I. Overview Currently, most automobile inner tubes use butyl rubber, or a blend of butyl rubber and other rubbers. Besides requiring high tensile and tear resistance, the rubber materials used in inner tubes also require good air tightness to ensure that the car does not need inflation for extended periods. To understand which manufacturing process produces which component of rubber with better air tightness, air tightness testing of the relevant products is necessary. The current industry standard test method is to fully inflate the entire inner tube, connect a pressure gauge, and observe the pressure drop over a period of time. Currently, besides observing the pressure drop, there is no other ideal way to implement this holistic testing method. This test method is inaccurate, time-consuming, and inconvenient to operate. GB/T 7755-2003 (Determination of air permeability of vulcanized or thermoplastic rubber) provides a method for testing the air tightness of rubber materials. This method can quickly and accurately determine which rubber has better air tightness, allowing for further calculations to determine which type of rubber makes the best-sealing inner tube for wheels. II. Brief Introduction to the GB/T 7755 Test Principle: As shown in the diagram below, a circular sample is placed in a temperature-controlled, permeable mold cavity. The sample divides the cavity into upper and lower parts. A certain pressure is applied to the upper cavity, allowing gas to penetrate the sample under pressure difference; this is also called the high-pressure side. The lower cavity is generally referred to as the low-pressure side. Connect the high-pressure side to a constant-pressure gas reservoir to ensure that the high-pressure side remains at a constant pressure throughout the test. Gas permeates through the sample to the low-pressure side, where the volume is always V. Therefore, the pressure increases from P to ΔP, and the volume of gas permeating to the low-pressure side is ΔV. The original gas volume is then compressed to V-ΔV. A high-precision pressure sensor monitors the pressure change ΔP on the low-pressure side, and the permeation amount ΔV can be calculated using the following formula: P•V=（P+ΔP）•（V-ΔV） III. Test Procedure 1. Carefully select a flat sample from the material to be tested, free from scratches, perforations, and surface attachments or other defects. Cut a circular sample of the required size from the sample. The maximum deviation of the sample thickness should not exceed 10% of the average thickness. 2. Clean the surface of the lower chamber with a soft material to remove dust or vacuum grease left from previous tests. 3. Apply a layer of vacuum grease evenly to the sealed area of ​​the lower chamber. 4. 5. Place the cut porous gasket on the low-pressure side as a support for the sample to resist the gas pressure load on the high-pressure side, ensuring that the sample does not deform significantly during the entire test. However, the porous gasket must not come into contact with the vacuum grease. 6. Place the sample flat, ensuring the porous gasket and sealing ring are as concentric as possible. 7. Combine the high-pressure and low-pressure chambers and maintain a sealed state. 8. Connect the high-pressure side of the permeability chamber to the gas storage bottle. Depending on the permeability of the sample, the test pressure can be set to 0.2MPa～0.5MPa. 9. Detect the pressure rise on the low-pressure side. IV. Application of GB/T 7755 Test Method in Automobile Inner Tubes The GB/T 7755 test method, when applied to the permeability testing of automobile inner tubes, can greatly improve testing accuracy and shorten testing time. The testing instrument used to perform this standard requires a very small volume on the low-pressure side, which is temporarily set to 12 ml in this paper. The sample penetration area is set to 36 cm², and the instrument's testing accuracy is 0.3 Pa. If the instrument detects a pressure change of 0.3 Pa on the low-pressure side, the gas permeation amount can be calculated using formula (1). In the formula, the pressure on the low-pressure side is P = 0.1 MPa, V = 12 ml, and ΔP = 0.3 Pa. Therefore, ΔV = 3.6 × 10⁻⁵ ml, meaning the volume on the low-pressure side increases by 3.6 × 10⁻⁵ ml. If the pressure on the high-pressure side is calculated as 0.2 MPa, then the gas loss on the high-pressure side is 1.8 × 10⁻⁵ ml. This value is the gas permeation amount on the high-pressure side over the 36 cm² sample area. The outer surface area of ​​a car inner tube is approximately 0.6 m². Based on the above calculation, its permeation amount is 0.003 ml. How much pressure drop will this permeation amount cause in a 22 L tire? The following formula can be used to calculate: P1•（V1-△V）=（P1-△P）•V1 Where P1=0.2MPa is the internal pressure of the inner tube; V1=22L is the volume of the inner tube; △V=0.003 ml is the leakage amount of the inner tube. Therefore, △P=0.0272Pa. This means that for the same material under the same testing conditions, when the GB/T 7755 test method can detect a pressure change of 0.3Pa, the traditional testing method can only detect a pressure change of 0.0272Pa. If one wants to detect a tire pressure change of 0.3Pa using the traditional method, it must take 11 times longer than the GB/T 7755 test method. Furthermore, considering that the pressure gauge used in the traditional method generally has a resolution of over 100Pa, when the tire pressure change reaches the minimum resolution of the pressure gauge (100Pa), the testing time will be more than 3600 times longer than the GB/T 7755 test method. Furthermore, the GB/T 7755 test method enables specific testing of specific materials. Its test results depend solely on the material itself and are unrelated to other factors, providing excellent guidance for the selection and improvement of inner tube materials. V. Conclusion To obtain high-quality products or accelerate product upgrades, in addition to continuous improvements in technology and processes, ideal testing methods are essential. Rapid and accurate data testing often plays a decisive role in research and production.