Heat shrinkage rate testing service

Heat Shrinkage Rate Testing Service – Accredited ISO/IEC 17025 Thermal Dimensional Stability Assessment for the Croatian Market

Heat shrinkage rate is a critical thermal property that quantifies the dimensional change of a material (typically polymeric films, tubes, sheets, cables, or fabrics) when exposed to elevated temperatures. This property directly influences the performance, fit, and reliability of heat‑shrinkable products used in electrical insulation, cable jacketing, packaging, automotive wiring, medical device manufacturing, and consumer goods. In the Croatian market, where the Hrvatski zavod za norme (HZN), the Ministarstvo gospodarstva i održivog razvoja, the Državni inspektorat, and the Carinska uprava enforce strict quality, safety, and performance standards aligned with EU directives and HRN EN (Croatian standards based on European norms), the accurate evaluation of heat shrinkage rate is essential for product certification, supplier qualification, quality control in manufacturing, and import‑export processes. Our laboratory offers a comprehensive heat shrinkage rate testing service, applying standardized methods such as ASTM D2732, ISO 14616, EN 60684‑2, and HRN EN 60684‑2 to measure free shrinkage, constrained shrinkage, and shrinkage force under controlled temperature conditions. All tests are performed under our ISO/IEC 17025 (CNAS) accreditation, and the resulting reports are fully accepted by Croatian authorities and notified bodies, making them indispensable for regulatory compliance, product validation, and market access in Croatia and the European Union.

Heat‑Shrinkable Material Samples We Regularly Test

Our laboratory receives a wide variety of heat‑shrinkable materials and products for shrinkage rate testing. Typical samples include:

• Heat‑shrinkable tubing and sleeving – polyolefin, PVC, fluoropolymer, and elastomeric tubing for electrical insulation and cable protection.
• Heat‑shrinkable films and sheets – for packaging, labeling, and shrink‑wrap applications.
• Heat‑shrinkable cables and wires – with cross‑linked insulation and jacketing layers.
• Heat‑shrinkable connectors and end caps – for sealing and terminating cables and wires.
• Heat‑shrinkable textiles and fabrics – for technical applications and protective covers.
• Prototype and new material formulations – submitted by manufacturers for validation of shrinkage performance before series production.
• Field‑retrieved heat‑shrinkable products – for failure analysis and remaining life assessment.

Free Shrinkage Rate Testing – Measuring Unrestrained Dimensional Change

Free shrinkage rate testing measures the percentage of dimensional change (typically in length, width, or diameter) of a material sample when it is heated to a specified temperature without any external restraint. This is the most common and fundamental test for evaluating the shrinkage performance of heat‑shrinkable materials. Our procedures follow international standards and the requirements of the Croatian electrical, packaging, and automotive sectors.

• Free shrinkage test for heat‑shrinkable tubing (ASTM D2732 / ISO 14616 / NTC 5700 – for tubing and sleeving) – we cut a sample of the tubing to a specified length (e.g., 100 mm) and mark its initial dimensions. The sample is placed in an oven (or a fluid bath) at the specified test temperature (typically 100 °C, 125 °C, 150 °C, or 175 °C) for a specified duration (typically 5, 10, 15, or 30 minutes). After the exposure, the sample is removed and allowed to cool to room temperature. The final dimensions are measured, and the free shrinkage rate (in %) is calculated as: (Initial dimension – Final dimension) / Initial dimension × 100. We report the free shrinkage rate (in %), the test temperature, the exposure time, and the dimensions.
• Free shrinkage test for heat‑shrinkable films (ASTM D2732 – for films and sheets) – we cut a square or rectangular specimen (e.g., 100 mm × 100 mm) from the film and mark the initial dimensions in both the machine direction (MD) and the transverse direction (TD). The specimen is heated in an oven (or a fluid bath) at the specified temperature for the specified time. After cooling, the final dimensions in both directions are measured. We report the free shrinkage rate in MD and TD, the test temperature, and the exposure time.
• Free shrinkage test at different temperatures (NTC 5701 – for the temperature‑shrinkage curve) – we perform the free shrinkage test at several temperatures (e.g., 80 °C, 100 °C, 125 °C, 150 °C, 175 °C) to construct the temperature‑shrinkage curve. The curve reveals the onset temperature, the maximum shrinkage, and the shrinkage rate as a function of the temperature. We report the temperature‑shrinkage curve and the key parameters (the onset temperature, the maximum shrinkage temperature, and the maximum shrinkage rate).
• Free shrinkage test at different times (NTC 5702 – for the shrinkage kinetics) – we perform the free shrinkage test at a fixed temperature (e.g., 150 °C) with different exposure times (e.g., 1, 2, 5, 10, 15, 30 minutes) to determine the shrinkage kinetics. The shrinkage vs. time curve is plotted. We report the shrinkage vs. time curve, the time to reach 50 % of the maximum shrinkage (t50), and the time to reach 90 % of the maximum shrinkage (t90).
• Free shrinkage test after aging (NTC 5703 – for the effect of aging on shrinkage) – we age the material (e.g., by thermal aging, UV exposure, or humidity exposure) and then measure the free shrinkage rate. The change in the shrinkage rate indicates a change in the polymer's molecular structure (e.g., cross‑linking or chain scission). We report the shrinkage rate before and after aging.
• Free shrinkage test for heat‑shrinkable textiles (NTC 5704 – for the shrinkage of fabrics) – we cut a fabric specimen (e.g., 100 mm × 100 mm) and heat it at the specified temperature. The shrinkage in both the warp and weft directions is measured. We report the shrinkage in warp and weft directions.

Constrained Shrinkage Force Testing – Measuring the Force Generated during Shrinkage

Constrained shrinkage force testing measures the force generated by the material when it is allowed to shrink against a restraint (i.e., when it is held at a fixed length). This force is critical for applications where the heat‑shrinkable material must apply a specific clamping force (e.g., in cable connectors, sealing caps, or strain relief sleeves).

• Shrinkage force test (ASTM D2732 – variant for force measurement, NTC 5710 – for tubing and sleeving) – we mount a sample of the tubing (or the film) in a tensile testing machine with a load cell (range 0‑500 N). The sample is heated to the specified test temperature (using a temperature‑controlled chamber or a hot air gun) and allowed to shrink while being held at a fixed length. The force generated by the shrinkage is measured continuously. The maximum force (in N) and the force profile are reported. We report the maximum shrinkage force, the force‑time curve, and the test temperature.
• Shrinkage force at different temperatures (NTC 5711 – for the temperature‑force curve) – we measure the shrinkage force at several temperatures (e.g., 80 °C, 100 °C, 125 °C, 150 °C) to construct the temperature‑force curve. The curve reveals the temperature at which the maximum force is generated. We report the temperature‑force curve and the peak force temperature.
• Shrinkage force relaxation test (NTC 5712 – for the long‑term force retention) – we measure the shrinkage force over an extended period (e.g., 1 hour, 24 hours) at a constant temperature. The decay of the force (the force relaxation) is measured. We report the force relaxation curve and the percentage of force retention after the specified time.
• Shrinkage force for different tube sizes (NTC 5713 – for the effect of wall thickness) – we measure the shrinkage force for tubing of different diameters and wall thicknesses. The force is normalized by the cross‑sectional area to obtain the shrinkage stress (in MPa). We report the shrinkage force and the shrinkage stress.
• Shrinkage force in constrained shrinkage (NTC 5714 – for the application‑specific force) – we simulate the actual application by mounting the tubing on a mandrel (or a cable) and measuring the force exerted on the mandrel during the shrinkage. The clamping force (in N) is reported. We report the clamping force and the effect on the mandrel.

Influence of Temperature and Heating Rate – Evaluating the Shrinkage Behavior

The shrinkage rate and the shrinkage force are highly dependent on the temperature and the heating rate. Our tests evaluate the effect of these parameters, providing essential data for the process optimization and the quality control of heat‑shrinkable products.

• Temperature sensitivity test (NTC 5720 – for the shrinkage vs. temperature curve) – we measure the free shrinkage rate at a range of temperatures (e.g., from 80 °C to 200 °C, in 10 °C increments) to generate the shrinkage vs. temperature curve. The curve is used to determine the optimum shrink temperature and the temperature range for the application. We report the shrinkage vs. temperature curve and the optimum shrink temperature.
• Heating rate effect (NTC 5721 – for the effect of the ramp rate) – we heat the sample to the specified temperature at different heating rates (e.g., 1 °C/min, 5 °C/min, 10 °C/min, 20 °C/min) and measure the final shrinkage. The effect of the heating rate on the shrinkage is evaluated. We report the shrinkage at each heating rate.
• Shrinkage at different oven temperatures (NTC 5722 – for the process validation) – we perform the free shrinkage test in ovens (or hot air ovens) at different set temperatures, to simulate the conditions of industrial drying and shrinking processes. We report the shrinkage rate at each oven temperature and the temperature uniformity.
• Shrinkage in fluid baths (NTC 5723 – for the high‑rate heating) – we perform the free shrinkage test in a silicone oil bath or a glycerin bath, which provides a more rapid and uniform heating than an oven. The test is performed at the specified temperature. We report the shrinkage rate and the heating rate.
• Effect of pre‑heating and conditioning (NTC 5724 – for the influence of the moisture content) – we condition the material at different humidity levels (e.g., 20 %, 50 %, 80 % RH) and then perform the free shrinkage test. The effect of the moisture content on the shrinkage is evaluated. We report the shrinkage rate at each humidity level.

Environmental and Aging Effects on Shrinkage – Evaluating Durability and Stability

The shrinkage performance of heat‑shrinkable materials can change over time due to thermal aging, UV exposure, chemical attack, and mechanical stress. Our environmental and aging tests evaluate the long‑term stability of the shrinkage properties, ensuring the reliability of the product over its service life in the diverse Croatian climate (coastal, continental, and mountainous).

• Thermal aging effect on shrinkage (ASTM D573 / ISO 188 / NTC 5730 – for the heat‑aged materials) – we age the material in an oven at a specified temperature (e.g., 100 °C) for a specified duration (e.g., 7, 14, 28 days) and then measure the free shrinkage rate. A decrease in the shrinkage rate indicates an additional cross‑linking of the polymer. We report the shrinkage rate before and after aging and the percentage change.
• UV aging effect on shrinkage (ASTM G154 / NTC 5731 – for the UV‑exposed materials) – we expose the material to UV radiation (UVA‑340) and condensation cycles for a specified duration (e.g., 500 hours) and then measure the free shrinkage rate. The effect of UV on the shrinkage is evaluated. We report the shrinkage rate after UV exposure and the change.
• Chemical exposure effect on shrinkage (ASTM D471 / NTC 5732 – for the chemically exposed materials) – we immerse the material in various chemicals (e.g., mineral oil, 10 % HCl, 10 % NaOH, or a solvent) for a specified duration (e.g., 7 days) and then measure the free shrinkage rate. The effect of the chemical on the shrinkage is reported. We report the shrinkage rate after chemical immersion and the compatibility.
• Humidity and moisture effect (NTC 5733 – for the moisture‑absorbed materials) – we condition the material at a high‑humidity environment (e.g., 40 °C, 95 % RH) for a specified duration (e.g., 7 days) and then measure the free shrinkage rate. The effect of moisture on the shrinkage is evaluated. We report the shrinkage rate after humidity exposure and the moisture uptake.
• Mechanical stress effect (NTC 5734 – for the pre‑stressed materials) – we apply a pre‑strain to the material (e.g., 10 % elongation) and then perform the free shrinkage test. The effect of the pre‑strain on the shrinkage is evaluated. We report the shrinkage rate with and without the pre‑strain.

Quality Control and Compliance Verification – Ensuring Conformity with Standards

The measured heat shrinkage rate is compared with the requirements of the relevant material standards and the customer specifications to determine the conformity of the product. Our tests provide a clear pass/fail result and a statement of compliance, which is essential for the certification of heat‑shrinkable products in the Croatian and EU markets.

• Compliance with HRN EN 60684‑2 (NTC 5740 – for the heat‑shrinkable tubing) – we compare the measured free shrinkage rate and the shrinkage force with the requirements of the HRN EN 60684‑2 standard (which is harmonized with the European EN 60684‑2 standard). The standard specifies the maximum allowable shrinkage and the minimum shrinkage force for different tubing types. We report the compliance and the pass/fail status.
• Compliance with customer specifications (NTC 5741 – for the contract‑specific requirements) – we compare the measured shrinkage rate with the values specified in the customer's purchase order or the design specification. The customer may specify a range (e.g., 3‑5 % shrinkage) or a maximum limit. We report the measured value and the margin relative to the limit.
• Guarantee verification (NTC 5742 – for the contractual purposes) – we test the material to verify that its shrinkage rate is within the guaranteed value specified in the contract. We report the measured value and the margin relative to the guarantee.
• Batch‑to‑batch consistency (NTC 5743 – for the supplier qualification) – we perform the shrinkage test on multiple samples from different batches of the same material, to assess the consistency of the shrinkage performance. We report the statistical parameters (the mean, the standard deviation, and the range) and the consistency rating.
• Comparison with certified reference materials (CRMs) – NTC 5744 – for the quality assurance) – we use certified reference materials (e.g., standard heat‑shrinkable tubing with known shrinkage) to verify the accuracy of the test system. We report the measurement of the CRM and the comparison with the certified value.

Complementary Tests – Mechanical and Thermal Property Evaluation

To fully characterize the heat‑shrinkable material and to understand the factors that influence the shrinkage, we perform complementary tests, including tensile strength, elongation, and differential scanning calorimetry (DSC). These tests help to explain the shrinkage behavior and to optimize the formulation.

• Tensile strength and elongation (ASTM D638 / ISO 527 / NTC 5750 – for the mechanical properties) – we measure the tensile strength (in MPa) and the elongation at break (in %) of the material before and after the shrinkage process. The change in the tensile properties is an indicator of the molecular orientation and the degree of cross‑linking. We report the tensile strength and the elongation before and after shrinkage.
• Differential scanning calorimetry (DSC) – ASTM D3418 / NTC 5751 – for the thermal transitions) – we measure the melting temperature (Tm) and the crystallinity (in %) of the material, using DSC. The melting temperature is related to the shrink temperature, and the crystallinity is related to the shrinkage force. We report the Tm and the crystallinity.
• Thermogravimetric analysis (TGA) – ASTM E1131 / NTC 5752 – for the thermal stability) – we measure the thermal stability of the material (the decomposition temperature and the mass loss) using TGA. The thermal stability is an indicator of the material's ability to withstand the shrink temperature. We report the decomposition temperature and the mass loss.
• Gel content and cross‑linking degree (NTC 5753 – for the determination of the cross‑link density) – we measure the gel content (the insoluble fraction of the polymer) using a solvent extraction method. The gel content is an indicator of the degree of cross‑linking, which affects the shrinkage. We report the gel content (in %).
• Shrinkage anisotropy measurement (NTC 5754 – for the directional shrinkage) – for films and sheets, we measure the shrinkage in both the machine direction (MD) and the transverse direction (TD), and we calculate the shrinkage anisotropy (the ratio of MD shrinkage to TD shrinkage). We report the MD shrinkage, the TD shrinkage, and the anisotropy ratio.

Test Report and Recognition in the Croatian Electrical, Packaging, and Automotive Sector

All procedures described are within the scope of our ISO/IEC 17025 accreditation, with equipment calibrated periodically (ovens, tensile test machines, DSC, TGA, etc.) and traceability to international standards (NIST, PTB). Our test reports are issued in English (with a Croatian summary available on request) and include:

• Full identification of the sample (manufacturer, product type, dimensions, and material composition).
• Detailed description of the test methods applied (ASTM/ISO/EN/HRN EN/NTC standards, test temperature, exposure time, and heating rate).
• Numerical results: free shrinkage rate (%), shrinkage force (N), maximum shrinkage temperature (°C), tensile strength (MPa), elongation (%), Tm (°C), and gel content (%).
• Graphical data: temperature‑shrinkage curves, force‑time curves, and DSC thermograms.
• Comparative tables against the values specified by the client or against the limits of the relevant standards (ASTM D2732, ISO 14616, HRN EN 60684‑2, and the requirements of the HZN, Ministarstvo gospodarstva, and Državni inspektorat).
• Photographs of the test specimens before and after the shrinkage, and the DSC/TGA curves.
• Recommendations for material selection, process optimization, and quality control measures to achieve the required shrinkage performance.
• Expanded uncertainty (k=2) for all key measurements, calculated according to the ISO/IEC 98‑3 Guide.

These reports are fully accepted by the Hrvatski zavod za norme (HZN) for the verification of product conformity, by the Ministarstvo gospodarstva i održivog razvoja for industrial material compliance, by the Državni inspektorat for market surveillance, and by the Carinska uprava (Croatian Customs) for tariff classification and quality verification in the import of heat‑shrinkable products. Additionally, we offer consulting services for the selection of heat‑shrinkable materials with optimal shrinkage performance, the design of shrink‑fit components, and the implementation of quality control programs for dimensional stability, contributing to the reliability, safety, and performance of electrical, packaging, and automotive products in the diverse and growing Croatian market.