The Myth of “Shrink Wrapping” in Hatch Failure

Written by Bob Peel, Greatlander

“Shrink wrapping” is one of the most commonly misused explanations for failed hatches.

It is often said that chicks become “shrink wrapped” because of low humidity during incubation or hatch, and that the membranes dry out and trap the chick.

What is usually being described is real—but the explanation is wrong.

What actually happens at the final stage of incubation

In the final stage before hatch, the embryo undergoes a normal and essential process known in hatchery terms as drawdown.

During this phase:

The embryo drinks the remaining albumen
Fluid levels inside the egg reduce as development completes
The yolk sac is gradually drawn into the body cavity
The air cell enlarges and becomes a respiratory space

This is not abnormal—it is a critical and expected stage of development.

In simple terms, the embryo is effectively using the remaining albumen as a nutrient and fluid source before hatch.

What people see and misinterpret

When a failed egg is opened, especially after cooling, observers often see:

Tight or collapsed membranes
A dry-looking inner shell surface
The chick positioned tightly within the air cell space
Reduced fluid compared to earlier stages

From this, it is easy to assume the chick has been “wrapped” or “stuck” by drying membranes.

However, what is being seen is usually the normal end-stage structure of a properly developing egg after drawdown.

Once the egg is opened and exposed to air, the internal environment also changes rapidly, which can further exaggerate the appearance of dryness or membrane adhesion.

Why the “shrink wrapping” explanation became popular

The term likely emerged because:

Failed hatches are emotionally difficult for breeders
Dry or tight membranes look like a mechanical constraint
Humidity is an easy variable to blame
The true internal developmental sequence is not well understood outside hatchery practice

So a visual observation was given a simple cause-and-effect explanation that seemed logical—but was not based on the actual biology or physics of incubation.

The engineering reality

From an engineering and developmental standpoint:

The embryo is not being physically “wrapped” by shrinking material
The membranes are not actively contracting onto the chick
The observed tightness is a result of normal fluid redistribution and absorption during final development

The system is one of gradual internal change, not external constriction.

The key distinction

The critical misunderstanding is this:

Normal drawdown = embryo consuming remaining albumen and preparing for hatch
Shrink wrapping (as commonly described) = assumed external mechanical constraint caused by humidity

In most cases, what is called “shrink wrapping” is actually normal developmental anatomy observed after a failed or incomplete hatch, often made more visible by post-mortem cooling and drying.

Why this matters

Misdiagnosing hatch failures leads to:

Incorrect humidity adjustments
Overcompensation in later hatches
Reinforcement of incorrect incubation practices

Understanding the actual biology prevents chasing the wrong variable.

Practical takeaway

Most cases described as “shrink wrapping” are not a humidity-induced mechanical failure.

They are the normal final-stage condition of an embryo that:

completed drawdown
reached internal pipping stage
but failed to progress to external hatch for other reasons