Will the paper cup deform or leak when used for cold or hot drinks

Paper cups are mainly composed of food-grade paper and anti-seepage coating. The most common paper is virgin wood pulp paper or paperboard, and its inner surface is usually covered with a layer of polyethylene (PE) or polylactic acid (PLA) coating to prevent liquid penetration. The bottom and body of the cup are heat-sealed or ultrasonically sealed to form a complete container structure.
According to different uses, paper cups are roughly divided into two categories: cold drink cups and hot drink cups. The two differ in structure, material thickness and anti-seepage performance design. Cold drink paper cups usually focus on moisture-proof and leak-proof performance, while hot drink paper cups require good heat resistance and cup body stiffness.

Deformation risk in hot drink environment
In hot drink application scenarios, paper cups need to withstand liquid temperatures as high as 60℃ to 100℃. If the paper cup is not properly selected or the manufacturing process is defective, it is easy to cause deformation, softening or even leakage.
Hot drink paper cups usually use thick paperboard with single PE or double PE coating as the material, and the cup wall thickness is between 0.3 and 0.6 mm. To improve heat resistance, paper cup manufacturers use high-stiffness base paper and control the curling forming temperature and time to form a stable structural support at the cup mouth.
Thermal stress is mainly concentrated at the seal between the cup mouth and the bottom of the cup. When hot liquid is contained for a long time, the hot melt layer of the cup bottom seal may relax stress or melt, resulting in micro cracks, which may cause leakage. In addition, if the cup body is heated unevenly during the production process, the sealing time is insufficient or the pressure is too small, it is also easy to lose structural integrity and deform under high temperature conditions.

Structural challenges in cold drink environments
Cold drinks are usually accompanied by ice cubes, and the liquid temperature is between 0℃ and 10℃. Although the temperature is lower and the risk of deformation is lower than that of hot drinks, paper cups need to face problems such as condensation erosion and softening of the cup body due to moisture.
Cold drink paper cups usually use double PE coated paper to provide stronger waterproof ability. The outer layer of PE prevents water vapor in the external air from condensing into water droplets and soaking the cup wall, while the inner layer of PE blocks beverage leakage. Some high-end paper cups use PLA biodegradable coatings. Although they are environmentally friendly, they may have the risk of physical performance degradation in long-term cold storage and low-temperature and high-humidity environments.
If cold drink paper cups use single PE paper or the coating is not airtight, condensed water can easily penetrate into the paper layer, causing the paper structure to collapse, leading to softening, collapse or seepage. Especially in high humidity environments, if the stacking, transportation or cold storage time is too long, the risk is further magnified.

Analysis of common causes of leakage
Paper cup leakage usually occurs at the junction of the bottom edge of the cup and the cup body. Insufficient heat sealing temperature, short time, uneven pressure or excessive moisture content of the paper may cause loose sealing or local gaps. After hot drink liquid penetrates into the gap, it can soften the edge of the paper and expand the leak.
In addition, the density of the paper substrate, fiber arrangement and the integrity of the coating will affect the permeability of the paper cup. If there are pinholes, damage or uneven thickness in the coating, the liquid may penetrate the surface layer into the cardboard in a short time, causing structural failure.
In the cold drink scenario, if the cup edge curling is not properly controlled, it is easy to "reverse curling" or "burr edge". These defects will cause the lid to not fit tightly and water droplets to be retained, which will indirectly cause local leakage or user experience problems.

Industry response strategies and technological progress
In order to deal with the deformation and leakage problems under hot and cold drinks, the industry generally adopts the following optimization measures:
Select base paper with high stiffness and high wet strength;
Apply multi-layer coating technology to improve anti-seepage ability;
Optimize the sealing temperature curve and hot pressing time;
Use double PE or PLA instead of single PE coating to improve the overall anti-seepage performance;
Introduce automatic equipment for curling detection and sealing integrity detection.