Resin Moisture Recording

This topic is part of the SG Systems Global plastics, resin conditioning and bulk material traceability glossary.

Updated December 2025 • Dryer Performance, Material Conditioning, MES/LIMS Integration • Plastic & Resin, Medical Devices, Consumer Products, Food Contact Packaging

Resin moisture recording is the systematic capture of measured moisture content for plastic resins (pellets or granules) at critical steps in the drying and molding process – tied to material lots, silos, dryers, presses and production orders. Rather than assuming the dryer is “good enough”, resin moisture recording creates time-stamped, lot-specific evidence in MES, LIMS or historians that resin actually met required moisture limits before being processed into parts that end up in BMR, eBMR or DHR flows.

“If your only proof that resin was dry enough is ‘the dryer was on’, you don’t have process control – you have optimism with heaters.”

1) What Resin Moisture Recording Actually Covers

Resin moisture recording is the structured proof that:

• Each critical resin type has a defined moisture specification and test method.
• Moisture is measured at appropriate points – often after drying and before molding or extrusion.
• Results are recorded against specific material lots, dryers, silos or day bins, not just “plant averages”.
• Out-of-spec results trigger clear actions – extended drying, segregation, blend limits or holds.

It is not just “we sometimes send a pellet sample to the lab.” It uses defined sampling plans, validated methods and integrated data capture so that moisture behaviour becomes part of normal process control rather than a forensic exercise after parts fail in the field.

2) Why Resin Moisture Recording Matters

For many hygroscopic resins – such as PET, PA, PC and certain blends – moisture content directly affects:

• Mechanical properties (impact strength, elongation, creep).
• Surface finish, splay, bubbles and other cosmetic defects.
• Dimensional stability and long-term performance.
• Hydrolytic degradation during processing at high melt temperatures.

Without credible resin moisture recording, it is difficult to separate issues caused by resin handling from those caused by tooling, cycle settings or downstream conditions. Customers and regulators are increasingly unwilling to accept “we think the resin was OK” as an explanation when brittle parts or stress cracking show up months after shipment.

3) Relationship to Drying, Conditioning and Bulk Handling

Resin moisture recording is tightly connected to:

• Dryers and conditioning: Drying time, temperature, dew point and airflow, often supported by temperature & humidity control.
• Silos and day bins: Moisture pick-up or loss during storage, as discussed under silo behaviour and flowability.
• Conveying: Hot air vs ambient transfer, line lengths and residence times.
• Weighing and dosing: Flow stability through loss-in-weight feeders and blending systems.

Moisture recording provides the feedback loop that confirms drying and storage practices actually deliver resin in the desired condition. Without it, dryers, desiccant systems and dew point alarms become unverified assumptions in the process rather than proven controls.

4) Core Building Blocks – Specs, Methods, Points and Systems

Effective resin moisture recording relies on four fundamentals:

• Specifications: Moisture limits by resin type, grade, application and product family.
• Methods: Defined test methods (e.g. loss-on-drying, Karl Fischer) with clear sample handling rules.
• Sampling points and frequency: Where and how often moisture is checked – silos, dryers, hoppers, line-side bins.
• Systems: A place to store and use the data – LIMS, MES, process historians or QMS forms.

Without clear specifications and sampling rules, moisture recording becomes random; without systems, it becomes disconnected – useful for a single lab report, but invisible to engineers planning runs or investigating scrap trends months later.

5) What Resin Moisture Recording Typically Captures

A robust resin moisture recording dataset will usually include:

• Material identity and grade, including supplier and internal item codes.
• Supplier lot number(s) and any internal material lot assignments.
• Sample location – silo, Gaylord, dryer hopper, line-side bin, day bin, etc.
• Dryer or conditioning parameters at the time of sampling (time, temperature, dew point where available).
• Moisture result with units, method and instrument ID.
• Result classification – within or outside specification, and which limit was applied.
• Linked job, batch, press or line where the resin will be used.

Ideally, moisture results are attached to the same genealogy objects used for batch genealogy and consumption – so that “which moisture history did this part see?” is a query, not a guessing game.

6) Risk-Based Resin Moisture Recording

Not every resin or application justifies the same intensity of moisture recording. A risk-based approach recognises that:

• Highly hygroscopic, mechanically critical resins (e.g. medical-grade PC or PA) need stricter limits and higher sampling frequencies.
• Non-hygroscopic or low-risk resins can be monitored more lightly, for example by lot or by shift rather than by batch.
• Applications with long-term liability (safety components, medical devices) justify heavier evidence requirements than short-lived consumer items.

Your resin moisture recording SOPs should reflect these differences explicitly in the QMS, not informally in the memories of process engineers. That way, sampling intensifies where failure consequences are high and remains manageable where risk is lower.

7) Roles & Responsibilities – Production, Lab, QA and Engineering

Clear roles are essential for reliable resin moisture recording:

• Production / operators: Take samples correctly and at the right time, log basic contextual data and act on on-line readings.
• Laboratory / QC: Run moisture tests according to validated methods and maintain instruments and calibration.
• QA: Approve specifications, review trends and define actions for out-of-specures.
• Engineering / process owners: Connect moisture data to scrap, rework and performance issues and adjust processes accordingly.

If everyone assumes that “the lab” or “the dryer tech” is looking after moisture, nobody systematically owns the recording and follow-up. That becomes obvious when a brittle-part complaint arrives and nobody can find more than a handful of ad hoc measurements for the relevant period.

8) Integration with LIMS, MES, WMS and Historians

Resin moisture recording becomes most useful when it is integrated across systems:

• LIMS: Stores test results, methods and instrument details, often linked to certificates of analysis.
• MES: Links moisture results to work orders, presses and batches via materials consumption recording.
• WMS: Tracks lot locations in silos, Gaylords and bins so moisture results can be tied to where the resin actually is.
• Historians / SCADA: Capture continuous dryer and environmental data that give context to individual moisture points.

In a mature setup, resin moisture can be viewed on the same dashboards as OEE, scrap and quality metrics – not just in separate lab reports that only a few people ever see.

9) Using Resin Moisture Recording in Investigations and CAPA

During deviations, complaints or nonconformance investigations, resin moisture recording should help to:

• Quickly answer whether suspect parts were molded from in-spec or out-of-spec moisture lots.
• Identify trends – rising moisture levels as dryers degrade or ambient conditions change.
• Correlate scrap types (splay, short shots, brittleness) with moisture excursions.
• Support CAPA actions such as new limits, improved sampling or better dryer maintenance.

When resin moisture records are missing or sparse, moisture often becomes the “suspect that got away” – widely blamed but never conclusively confirmed or ruled out. Structured recording converts hunches into evidence, for better or worse.

10) KPIs and Continuous Improvement for Resin Moisture Recording

Resin moisture recording can be monitored with practical KPIs such as:

• Percentage of required moisture checks completed on time by resin and line.
• Rate of moisture-related deviations or scrap events per period.
• Average and worst-case deviation from target moisture by resin family.
• Investigation cycle time when moisture is a suspected factor.
• Number of batches processed under documented moisture excursions and how they were dispositioned.

These indicators help distinguish between plants that “sometimes measure moisture” and plants that use resin moisture recording as a real control lever – adjusting processes, maintenance and supplier expectations based on hard data rather than anecdote.

11) Common Failure Modes and Red Flags

Weak resin moisture recording tends to show up in similar ways across sites:

• Moisture specifications exist but are not reflected in day-to-day instructions or screens.
• Sampling is done only when a problem is obvious, not routinely as part of control.
• Results kept on local spreadsheets or paper logs, disconnected from genealogy and batch records.
• No clear distinction between “in-spec but high” and “truly out-of-spec” moisture bands.
• Frequent debate about whether resin was really dry at the time of molding – with no data to settle the question.

Auditors and customers see these as signs that resin handling is not truly under control, even if scrap is being managed reactively. In regulated or high-liability applications, that can trigger deeper scrutiny of incoming materials, dryers, silos and documentation practices more broadly.

12) Digitalisation & Industry 4.0 – Online Sensors and Models

In an Industry 4.0 context, resin moisture recording is increasingly supported by:

• On-line moisture sensors in hoppers, conveying lines or dryers feeding continuous data to SCADA and historians.
• Models that predict moisture behaviour based on dryer settings, throughput and ambient conditions.
• Alerts when moisture drifts toward limits, allowing pre-emptive action before scrap rises.

However, more data is not automatically better. Without validated sensors, clear specifications and aligned SOPs, online moisture data can confuse rather than clarify. The fundamentals – sampling discipline, clear limits and integration into decisions – still matter more than the technology used to collect the numbers.

13) FAQ

Q1. Do we need resin moisture recording for every resin we use?
Not necessarily at the same level of intensity. Highly hygroscopic resins and critical applications should have robust resin moisture recording with clear specs and frequent checks. Less sensitive resins can be monitored with lighter regimes, but completely ignoring moisture leaves a significant blind spot, especially as product and customer requirements evolve.

Q2. Is laboratory testing always required, or are on-line sensors enough?
On-line sensors are valuable for trends and alerts, but they usually need to be supported by periodic laboratory tests. Lab-based resin moisture recording provides traceable, method-defined results that can be referenced in investigations and regulatory submissions. Many sites use a hybrid approach – on-line readings for real-time control, lab tests for confirmation and calibration.

Q3. How often should we measure moisture for a given resin?
Frequency should be risk-based. Factors include resin hygroscopicity, application criticality, historical stability and process capability. Some plants sample by lot and shift; others require checks at job start, after downtime, or whenever dryers are adjusted. The key is to document the sampling plan in the QMS and verify that the plan is actually followed in practice.

Q4. How does resin moisture recording handle blends and masterbatch?
For blends and masterbatch, each component may have its own moisture behaviour and specification. Resin moisture recording should capture which components were conditioned and at what levels, then document the resulting blend moisture. In some cases, it is enough to control moisture on the base resin; in others, especially where hygroscopic additives are used, broader coverage is needed. The decisions should be explicit, not left to habit.

Q5. Where should we start if we currently rely on “dryer OK” lights instead of data?
A practical starting point is to identify one or two high-risk resin grades and define clear moisture limits and test methods for them. Implement simple resin moisture recording at dryer discharge or line-side bins for those grades, store the results in MES or LIMS and link them to lots and jobs. Once you see how often moisture approaches limits and how it correlates with scrap or complaints, you can refine specs, extend coverage and justify targeted investments in sensors or better dryers.

Related Reading
• Conditioning & Flow: Powder Conditioning – Temperature & Humidity Control | Powder Flowability Index | Fines and Coarse Particle Distribution | Loss-in-Weight Feeder Calibration
• Traceability & Records: Material Lot Assignment | Batch Genealogy | Traceability & End-to-End Lot Genealogy | Batch Manufacturing Record (BMR) | Electronic Batch Record (eBMR)
• Systems & Governance: MES – Manufacturing Execution System | Manufacturing Data Historian | Statistical Process Control (SPC) | Quality Management System (QMS) | Deviation / Nonconformance (NC) | CAPA