Does a hot-water cup deform? Let’s talk about the “heat resistance” of different plastics.

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When hot water is poured into disposable plastic cups, some hold up just fine, while others collapse, deform, or even leak. The key lies in the “plastic lineage” of the cups: their heat resistance varies dramatically.

As an equipment manufacturer deeply involved in the entire value chain from sheet material to finished products, we fully understand: The birth of a great product begins with a deep understanding of materials and is realized through processes and equipment that are perfectly matched to those materials.

I. The “thermal-resistance ID card” of plastics: the glass transition temperature

A core metric that determines whether a plastic is “heat-resistant” is called Glass transition temperature You can think of it as the “yield point” of plastic:

01. Below this temperature , the material retains the rigidity and hardness of the glassy state.

02. Higher than this temperature , the material gradually transitions into a rubbery state and begins to soften and deform.

The height of this “critical point” varies among different materials, directly determining the maximum temperature of beverages they can safely contain.

II. Ranking of “Heat Resistance” for Plastics Used in Mainstream Cups

01. PP (Polypropylene): The Heat-Resistant “Pragmatist”

①. Temperament : Exhibits excellent heat resistance and is the primary material for manufacturing “microwave-safe” food containers and heat-resistant cups. It typically withstands temperatures above 100°C for extended periods and can tolerate short-term exposure to 120–130°C.

②. Characteristics : It has a soft yet resilient feel and a waxy texture, often appearing semi-transparent or white. Cups made from this material are relatively safe for holding hot water and for heating in the microwave.

③. Our Perspective : Producing high-quality PP cups, for Uniformity of cooling and shaping of the sheet and Temperature control accuracy of the cup-making machine The requirements are extremely stringent. Our equipment ensures that PP material achieves complete crystallization during processing, thereby maximizing its heat resistance.

02, PS (Polystyrene): A Brittle “Cold Beauty”

①. Temper : Poor heat resistance—standard PS has a heat deflection temperature of about 70–90°C. When filled with hot water, it easily softens significantly; moreover, high-transparency PS (GPPS) cups may even crack due to internal stresses when exposed to boiling water.

②. Characteristics : High transparency and a crisp, ringing sound when tapped, but a brittle texture. Commonly used for serving cold drinks and yogurt.

③. Our Perspective : The key to producing PS cups lies in Gentle, uniform heating and Rapid cooling and shaping , to reduce internal stresses and mitigate its inherent brittleness. Our servo system delivers exceptionally smooth heating and mold-closing cycles.

03, PET (Polyethylene Terephthalate): A Sturdy “Tough Guy”

①. Temper : Heat resistance is better than PS but not as good as PP, with a typical range of about 65–85°C. Commonly used for “crystal”-textured beverage cups, it is suitable for hot coffee and milk tea, but may deform if used for extended periods with scalding hot water.

②. Characteristics : High hardness, excellent luster, crisp sound, and good gas barrier properties.

③. Our Perspective : PET is highly hygroscopic and has a narrow processing temperature window. This poses Drying System for Sheet Production and Temperature Control Stability in the Cup-Making Process Stringent requirements have been imposed. Our equipment delivers precise temperature-zone control, ensuring that PET is molded under optimal conditions.

III. From Material Characteristics to “Tailored” Production Equipment

Once you understand the material’s thermal resistance, it becomes clear why producing cups from different materials requires equipment that is “tailored to the specific needs”:

1. For “delicate” materials (such as PET and PLA) ：

①. Need : Extreme temperature-control precision and stable molding pressure. A temperature difference of just a few degrees can cause PET to turn white or degrade.

②. How do we proceed? : Our Fully Servo Cup-Making Machine Leveraging the precise drive and control capabilities of servo motors, it achieves millimeter-level precision in every stage—heating, mold closing, and pressure holding—thereby providing the most stable processing environment for sensitive materials.

2. For materials and structures that “require significant effort” (such as thick-walled PP cups and complex meal boxes) ：

①. Need : A substantial, stable, and sustained molding pressure ensures that the material fully fills the mold cavity and rapidly cools and sets, thereby enhancing its ultimate heat resistance.

②. How do we proceed? : Our Hydraulic Cup-Making Machine It delivers rock-solid, robust clamping force, ensuring uniform density and dimensional stability in thick-walled and complex-shaped parts, thereby fulfilling their designed thermal-performance requirements.

3. Control at the source (sheet material is key) ：

① A sheet with uneven crystallinity, internal stresses, or excessive moisture content is bound to fail in producing a high-heat-resistant cup.

②. How do we proceed? : Independently developed and manufactured by us Sheet-making machine Equipped with a sophisticated temperature-control system and screw design, it can tailor high-quality sheets with uniform thickness and stable performance to suit different materials—this is the first cornerstone of quality for a great cup.

IV. Conclusion

A cup of hot water tests not only the resilience of plastic, but also the entire process—from a single raw material to a piece of equipment and finally to a finished product. End-to-end cognitive and control capabilities 。

At Shantou Xinhua Packaging Machinery, we are not merely equipment manufacturers; we are also researchers of material properties and providers of process solutions. We understand that only by thoroughly grasping the heat resistance of PP, the brittleness of PS, and the sensitivity of PET—and by integrating these characteristics into our equipment design and control logic—can we deliver machines that reliably produce high-quality cups capable of withstanding hot water without deforming.

Understand materials—and even more, know how to make the most of them. 。 This is precisely the ultimate goal of all our science communication and technological research.

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