How Aerospace Manufacturers Track Prepreg Out-Time

A roll of carbon fiber prepreg can look unchanged from the day it was manufactured. But once it leaves controlled storage, its usable out-time begins to accumulate. For aerospace manufacturers working with time- and temperature-sensitive (TATS) materials, tracking that exposure is an important part of material control and traceability.

Out-time is the cumulative time a material spends outside its required storage conditions before it is used. The allowable limit depends on the specific material and its manufacturer's approved data sheet or technical documentation.

This post covers what out-time means, why it accumulates, what can happen when it is exceeded, and how controlled cold storage supports better material management.

What "Out-Time" Actually Means

Prepreg is carbon fiber or fiberglass pre-impregnated with an uncured resin system. It is stored under controlled temperature conditions to slow the resin's cure reaction and preserve the material's approved working life.

The required storage temperature is not universal. Each prepreg or adhesive system has its own manufacturer-specified storage conditions, shelf life, and allowable out-life. The applicable product data sheet and technical documentation should control those requirements.

Out-time is the cumulative amount of time material spends outside its required storage conditions. Once a roll leaves controlled storage, exposure begins to accumulate. Resin advancement can affect properties such as tack and drape as the material approaches its approved out-life.

Out-time is cumulative. If a roll is outside controlled storage for two hours on Monday and another 90 minutes on Thursday, the total exposure is three and a half hours. Returning the material to cold storage does not erase the time already accumulated.

That makes accurate time records important. The material's approved out-life should be checked against its actual exposure history before it is used.

Why Losing Track Is So Expensive

Out-time cannot be determined reliably by looking at a roll. Material that has exceeded its approved exposure limit may not look different from material that remains within specification.

That creates a documentation and quality-control problem. If exposure records are incomplete, a manufacturer may have difficulty determining whether material remained within its approved limits.

For aerospace composite operations, the consequences can include:

• Material loss. Material that exceeds its approved out-life may no longer be eligible for production use.
• Labor and cycle-time loss. Layup, bagging, curing, inspection, and other production work can be affected if material is later found to be outside its approved requirements.
• Traceability problems. Incomplete out-time records can make it harder to establish which parts were produced from a specific material lot or roll.

Accurate records help the production and quality teams determine the material's status before it reaches the next stage of manufacturing.

The Records Your Process Needs

Out-time requirements vary by material, customer, program, and applicable quality documentation. Rather than applying one universal storage or tracking rule, the process should follow the requirements established for the specific material being handled.

In practice, an effective recordkeeping process should capture:

• The date and time material leaves controlled storage
• Each subsequent out-time event
• The cumulative exposure time
• The material's approved out-life or exposure limit
• The status of the material before it is released for production
• A traceable connection between the material record and the parts or work orders using it

The level of documentation required should be based on the applicable material documentation, customer requirements, and the manufacturer's quality system.

Where Manual Tracking Breaks Down

Paper tags, whiteboards, and spreadsheets can record out-time, but they depend on consistent human input. Small gaps can create larger traceability problems.

Common failure points include:

• A tag is updated after an event instead of when it occurs.
• A roll is removed for a short inspection and the exposure is not recorded.
• A handwritten time or identification number is entered incorrectly.
• Material remains outside controlled storage during a shift change without a clear record of who is tracking it.

These are simple process issues, but they can make the material history harder to verify.

A reliable process makes each exposure event easy to record and gives production and quality teams a clear cumulative total.

Cold Storage Discipline Supports Out-Time Control

Out-time management begins before material reaches the production floor. The storage system needs to maintain the conditions specified for the material and provide records that can be reviewed when needed.

Several controls are particularly important:

• Correct storage temperature. Follow the temperature specified in the applicable manufacturer's data sheet for each material. Storage requirements differ between resin systems, prepregs, and adhesives.
• Documented intake and release. Record when material enters and leaves controlled storage so its movement can be traced.
• Continuous monitoring. Temperature monitoring provides a record of storage conditions and can help identify excursions that may require evaluation.
• Alarm and response procedures. A defined response process helps the team identify and address temperature excursions before releasing affected material.
• Backup planning. A contingency plan for equipment failure can reduce the risk of losing temperature-sensitive inventory or production time.

Cold storage does not replace out-time tracking. It supports it by maintaining the material under its approved storage conditions and creating a documented history of those conditions.

Building an Audit-Ready Out-Time Program

A strong out-time program connects storage records, material identification, and production records.

Component	What It Needs to Show
Storage conditions	Temperature records for storage equipment holding TATS material, including applicable alarm or excursion history
Intake and release records	Time-stamped records for material entering and leaving controlled storage
Cumulative out-time	Running exposure total for each material, checked against its approved limit
Excursion handling	Documented process for evaluating material affected by a storage or exposure event
Traceability	A clear connection between the material's history and the parts, work orders, or production records associated with it

The policy defines what the team needs to track. The tracking system provides the records needed to carry out that process consistently.

For facilities handling significant volumes of temperature-sensitive aerospace materials, controlled cold storage can make this process easier to manage by providing reliable temperature records, alarms, and documented storage conditions.

FAQ

What is "out-time" in composite manufacturing?

Out-time is the cumulative time a time- and temperature-sensitive material, such as prepreg, spends outside its required controlled storage conditions. The allowable exposure period depends on the specific material manufacturer's documentation.

Does putting material back in the freezer reset the out-time clock?

No. Returning material to its required storage conditions does not erase exposure that has already occurred. The cumulative out-time should continue to be measured according to the material manufacturer's requirements.

What happens if a part is made with material that exceeded its out-time limit?

The material may no longer meet the applicable requirements for production use. The appropriate response depends on the material documentation, customer requirements, and the manufacturer's quality procedures. It may require evaluation, rejection, or additional review.

What determines how much out-time a material is allowed?

The allowable out-time is specific to the material. The manufacturer's technical data sheet, handling instructions, and applicable customer or program requirements should be used to determine the approved exposure limit.

How does cold storage relate to out-time management?

Cold storage maintains materials under their specified storage conditions before and between production activities. Reliable temperature monitoring and documented material movement also provide records that support material traceability and out-time management.

The Bottom Line

Out-time is a measurable part of handling time- and temperature-sensitive aerospace materials. It accumulates as material is exposed outside its required storage conditions, and the allowable limit depends on the specific material.

Accurate tracking gives production and quality teams a clear record of that exposure. Controlled cold storage supports the process by maintaining specified conditions, monitoring temperature, and documenting storage history.

If your team is evaluating its current cold storage setup or material monitoring process, Ultracold Storage Solutions can help you review the storage requirements that apply to your temperature-sensitive materials.

Browse our laboratory freezer and refrigeration solutions, or request a quote to discuss your current setup with our team.