Inspection is the most common issue encountered. The weight of the hot water bag varies. It's not due to any shortcuts taken, but rather a normal practice in the industry. The main reasons are all related to production and raw materials.
Ⅰ. The raw materials themselves have a weight difference.
Due to differences in rubber/silicone batches, there are variations in density.
For natural rubber and synthetic rubber, the content of rubber, hardness, and density vary from batch to batch. Even with the same formula and mold, the weight can differ by a few grams.
Fluctuations in oil prices and rubber prices lead manufacturers to slightly adjust the formula.
When the price of rubber rises, some manufacturers will slightly modify the proportion of fillers, resulting in a change in density and thus a change in weight. This is a normal operation within the industry.
II. The production process cannot be absolutely consistent.
1
During each step of mixing, extrusion and molding, there are slight deviations.
The thickness of the rubber compound and the filling volume cannot be 100% consistent. Therefore, the final weight of the product is naturally subject to fluctuations.
2
Minor differences in vulcanization time and temperature
can result in different rubber contraction rates. It is normal for it to be slightly lighter or heavier.
III. Different styles, sizes and thicknesses
The thickness difference is just 0.1mm, but the overall weight is significantly different.
IV. Testing, Certification and Standard Requirements
Many countries (especially the EU) only require compliance with safety, tensile strength, leakage, and aging standards, and do not mandate uniform weight.
Therefore, in the industry, the general requirement is to meet the weight range standards, rather than a single point value.
Here is a practical conclusion for foreign trade:
The hot water bag is allowed a reasonable weight deviation. As long as it is within the agreed range and passes the test, it is a qualified product.
