A Comprehensive Guide to Moisture Protection with Plastic Film During the Rainy Season: A Practical Handbook for Storage and Production

Preface

During the plum rain season and flood period, the climatic conditions of high temperature, high humidity, and large diurnal temperature variations pose a hidden challenge for the film industry. The industry-standard safe humidity level for warehouse storage is 40%–60% , and during the rainy season, ambient humidity often exceeds 70% , which can easily cause the film to absorb moisture and deteriorate.

From warehouse film rolls sticking together and developing mold, to in‑process printing and lamination producing batch‑level rejects, and further to degraded end‑product performance and customer complaints, the losses caused by humid weather have long been a persistent challenge for many film‑manufacturing companies. Different film materials exhibit vastly varying moisture‑absorption characteristics—nylon, EVOH 、 TPU Functional membrane materials, in particular, are especially vulnerable to moisture damage.

This paper, drawing on industry best practices and relevant standards, examines from… Material pain points, warehouse management and control, manufacturing processes, transportation applications, and common pitfalls and misconceptions Drawing on five key dimensions, we have developed a practical, immediately implementable moisture‑control plan for the rainy season, helping membrane‑material manufacturers reduce scrap rates, ensure consistent product quality, and smoothly navigate the rainy‑season production cycle.

I. Core Pain Points of Film Moisture Absorption During the Rainy Season

Different material films have distinct molecular structures, resulting in markedly varying moisture resistance; moisture‑induced failures also differ in their specific failure modes. Precise differentiation is essential for targeted protection.

1. Nylon film ( BOPA ) —— Severely affected by dampness during the rainy season

Nylon’s polar molecules readily absorb moisture, and in high-humidity environments, this can lead to issues such as wrinkling on the film surface, unstable tension, and misregistration. When used for laminating or retort packaging, it is prone to defects like white spots, delamination, and reduced peel strength; in severe cases, these problems can cause retort pouches to rupture and become scrap, making nylon a critical focus of quality control during the rainy season in flexible packaging.

2. TPU thin film —— Prone to hydrolytic degradation

Prolonged exposure to a humid environment, TPU Hydrolysis reactions may occur, leading to chain scission and resulting in issues such as softening and tackiness of the film, dimensional swelling, and degradation of elasticity and abrasion resistance. Used for outdoor waterproofing, footwear materials, and electrical insulation. TPU Membranes experience a significant reduction in service life when exposed to moisture, leading to the immediate loss of their functionality.

3. High-barrier composite film —— A precipitous drop in protective performance

Contains EVOH Aluminum foil’s high-barrier film is extremely sensitive to moisture. EVOH Once the material absorbs moisture, its oxygen- and water-barrier properties deteriorate significantly. Meanwhile, the aluminum foil layer readily oxidizes and turns black or develops blisters when exposed to moisture, completely losing its barrier function and thereby shortening the shelf life of food and pharmaceutical packaging.

4. PE/PP Ordinary film —— Prone to adhesion and brittle fracture

In high-temperature, high-humidity environments, PE 、 PP The film tends to soften and stick together, making it impossible to unwind and process properly; in low‑temperature, rainy conditions, the material becomes brittle, leading to easy breakage during stretching and a sharp increase in damage rates during transportation and bag‑making. Moreover, food‑grade films are prone to mold growth, failing to meet regulatory standards.

5. Functional coating film —— Functional failure and scrapping

Functional films such as release liners, antistatic films, and antibacterial films are prone to delamination and loss of performance when their surface coatings become damp; this leads to imbalances in release force and the disappearance of antistatic properties, directly impacting the yield of electronic die-cutting and precision packaging processes.

II. Warehouse Moisture Control: Preventing Film Rolls from Reabsorbing Moisture and Deteriorating at the Source

Warehousing is the first line of defense against moisture for films. 90% The root cause of moisture‑induced film degradation lies in inadequate warehouse management and control. In accordance with industry standards, the warehouse environment must maintain a stable temperature. 15–25℃ , humidity 40%–65% , prevent condensation and moisture absorption.

1. Hardware moisture-proof modification

All film rolls must be elevated on pallets. 15cm In addition, prevent ground‑borne moisture from penetrating; direct stacking on the floor is strictly prohibited. In high‑humidity areas, warehouses must be equipped with dehumidifiers to maintain stable humidity around the clock and eliminate excessively damp conditions. Ensure that doors and windows are tightly sealed, and close ventilation openings during rainy weather to prevent outdoor moisture from entering.

2. Standardized Stacking Management

The stacking height of membrane rolls shall not exceed 1.5 Rice should be protected from crushing and deformation, with ventilation gaps left between stacks to prevent dampness and moisture buildup; implement zoned storage, nylon film, EVOH Highly hygroscopic materials, such as composite films, shall be stored separately and issued on a first‑in‑first‑out basis to minimize the risk of moisture damage to inventory.

3. Daily inventory management

Strictly adhere to the first‑in, first‑out principle to prevent long‑term storage from causing moisture damage to film rolls; record warehouse temperature and humidity data daily and promptly adjust dehumidification equipment; seal any unused leftover film and opened film materials with aluminum‑foil waterproof packaging to isolate them from air and moisture.

III. Workshop Production: Fine-tuning Processes to Prevent Batch Defects

During the rainy season, the significant diurnal temperature variation in the workshop can easily lead to invisible condensation on the film surface, which is a primary cause of recurring quality issues in printing, lamination, and bag‑making processes. Targeted process adjustments are therefore required.

1. Workshop Environmental Control

The core workshops for printing, lamination, and coating must maintain constant temperature and humidity, with the temperature kept stable at… 23°C Around, with humidity strictly controlled at 60% Inside; during humid weather, do not open windows for ventilation—rely on dehumidification equipment to control humidity and prevent condensation and water accumulation on the membrane surface.

2. Raw Material Pre-processing Control

Nylon films, high-barrier films, and other hygroscopic materials must undergo pre‑heating and drying before being fed into the machine to thoroughly remove moisture from both the film surface and between layers. Moisture‑affected film rolls must not be directly processed on the production line; this preventive measure helps avoid issues such as delamination, ink peeling, and misregistration at the source.

3. Production Process Adaptation and Adjustment

During the rainy season, appropriately optimize the ink-to-curing-agent ratio to enhance coating adhesion in humid conditions; reduce the production line speed to minimize web tension fluctuations and prevent defects such as slippage, wrinkling, and edge curling; and perform regular cleaning of equipment rollers to prevent moisture‑induced buildup that could compromise production accuracy.

IV. Transportation and End-Use Applications: End-to-End Moisture Protection

In addition to warehousing and production, proper protection during transportation in the rainy season and at outdoor application sites is equally critical to ensuring the quality of finished films and preventing losses at the final stage.

1. Logistics and Transportation Protection

During the rainy season, when transporting goods over long distances, cover the entire vehicle with a waterproof tarpaulin and wrap the exterior of the film rolls in water‑proof packaging and protective stretch film. Avoid leaving vehicles parked outdoors for extended periods to prevent rainwater infiltration and condensation caused by temperature differences, which can lead to moisture damage to the film rolls.

2. Outdoor Membrane Material Maintenance

Greenhouse film, outdoor waterproofing TPU For outdoor materials such as membranes, promptly remove standing water from the membrane surface after rain and clear surrounding drainage channels to minimize tensile deformation. Repair any tears or punctures without delay to prevent rainwater from penetrating the membrane layer and accelerating aging and further damage.

3. Terminal Storage Guidelines

Downstream finished packaging films and functional film materials must not be stacked against walls or on the floor upon receipt; they should be stored away from cool, damp corners in a dry, well-ventilated environment to prevent mold growth and performance degradation.

V. Common Misconceptions About High-Frequency Moisture Protection in the Industry: How to Avoid Pitfalls Precisely

Many companies experience poor moisture‑proofing during the rainy season—not because they lack protective measures, but because they fall into improper practices that end up exacerbating damage.

1.  Misconception 1: If the outer packaging is intact, the membrane material will not get damp.

Wrong! Standard packaging cannot prevent moisture penetration. In the high-humidity conditions of the rainy season, air can seep into the interior of the film roll through gaps in the packaging, and even with long-term storage, interlayer moisture absorption and sticking issues will still occur.

2. Misconception #2: For film rolls that have only slightly absorbed moisture, simply drying them in the sun will make them reusable.

Wrong! Nylon, TPU 、 EVOH Once the material has absorbed moisture, its molecular structure is already altered; drying it in the sun can only remove surface moisture and cannot restore its original peel strength or barrier performance, so defective products will still result during production.

3. Misconception #3: Thickening the plastic film will effectively resist moisture.

Wrong! The moisture resistance and hydrolytic stability of a thin film are determined by its material formulation, not its thickness; simply increasing the thickness will not address core issues such as moisture absorption, hydrolysis, or oxidation.

4.  Misconception 4: Opening windows for ventilation on rainy days can reduce indoor humidity.

Wrong! During the rainy season, outdoor air humidity is far higher than indoor humidity. Opening windows will let in large amounts of moisture, exacerbating dampness in workshops and warehouses. The best approach is to keep spaces sealed. + Equipment dehumidification.

Conclusion

During the rainy season, moisture‑proofing with plastic film is not a temporary emergency measure; it is a routine quality‑control practice that spans warehousing, production, transportation, and the point of sale. In high‑humidity conditions, different film materials exhibit distinct susceptibility to moisture, and haphazard protective measures not only waste resources but can also lead to batch defects and inventory write‑offs.

For membrane‑material manufacturers, only by thoroughly understanding the moisture‑absorption characteristics of each type of film, implementing standardized moisture‑control procedures, and making targeted optimizations to production and storage processes can they minimize losses during the rainy season, ensure consistent product quality, and reduce customer complaints. As extremely humid weather becomes increasingly commonplace, Moisture-resistant, hydrolysis-resistant, highly stable Modified films will also become a key trend driving industry differentiation and upgrading.

Effective moisture‑control management during the rainy season not only safeguards product quality but also serves as a key driver for cost reduction, efficiency gains, and enhanced market competitiveness.