Why Humidity Control Matters in Glass Display Cases — And What Specifiers Need to Consider

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In museums, galleries, archives, and private collections, a glass display case is far more than a transparent enclosure. It is a microclimate—one that can either preserve precious objects for generations or quietly accelerate their deterioration. While lighting, security, and aesthetics often receive the most attention, humidity control remains one of the most critical and frequently misunderstood aspects of display case design.

For specifiers, understanding the role of humidity control—and selecting the correct approach—is essential to achieving long-term conservation performance, operational efficiency, and risk reduction.

The Hidden Threat: Why Relative Humidity Matters

Organic materials such as wood, textiles, ivory, paper, leather, and some metals are highly sensitive to moisture. Excess humidity encourages mould growth, corrosion, and dimensional distortion, while low humidity can cause embrittlement, cracking, and shrinkage. Even minor fluctuations in relative humidity (RH) can introduce internal stresses that lead to cumulative, irreversible damage.

A display case therefore functions as a stabilising envelope, shielding objects from daily and seasonal environmental changes. The effectiveness of that envelope depends entirely on whether—and how—humidity is controlled.

Buffered, Mechanical, or No Control? What the Arts Council Recommends

Arts Council guidance requires specifiers to answer a fundamental question at an early stage:

Do display cases require passive (buffered) humidity control, mechanical (active) control, or no dedicated control at all?

Each approach has clear advantages and limitations, and the correct choice depends on object sensitivity, risk tolerance, and operational capacity.

1. Passive (Buffered) Humidity Control

Passive systems rely on humidity buffer materials such as ArtSorb sheet silica gel or granular silica gel. These materials absorb or release moisture to maintain stable RH conditions within a sealed case.

Key guidance includes:

  • Approximately 20 kg of silica gel per cubic metre of display volume as a baseline.
  • Reduction to around 2.5 kg per cubic metre where cases demonstrate exceptionally high air-tightness.
  • Installation with maximum exposed surface area facing the display volume.
  • Provision for renewal or regeneration without disturbing displayed objects.

When to choose passive control:

  • For most environmentally sensitive collections.
  • Where active systems are unnecessary or impractical.
  • When long-term stability with low maintenance requirements is preferred.

2. Mechanical (Active) Humidity Control

Mechanical systems regulate RH using powered equipment such as ducted air systems, dehumidifiers, or humidifiers. These systems actively adjust environmental conditions inside the case.

The Arts Council identifies several drawbacks:

  • Requirement for plant space and ductwork, often disruptive to install.
  • Higher maintenance costs and cleaning complexity.
  • Greater susceptibility to mechanical failure.
  • A shorter operational lifespan compared to passive systems.

When to choose active control:

  • When objects have extremely narrow environmental tolerances.
  • When a microclimate must be maintained independently of gallery conditions.
  • When sufficient technical resources and maintenance infrastructure are available.

3. When No Dedicated Humidity Control Is Needed

Not all collections require specialised RH stabilisation. A well-engineered, airtight display case located within a gallery already maintained for human comfort can often provide adequate buffering against short-term fluctuations.

This approach may be suitable for:

  • Durable materials such as ceramics, glass, and some metals.
  • Short-term or temporary exhibitions.
  • Institutions with consistently stable ambient environmental control.

Why Specifiers Should Consider Humidity Control Early

Humidity control should be addressed at the outset of any display case specification for several reasons:

  1. It shapes case design and construction. Airtightness targets, gasket selection, material choices, ventilation pathways, and maintenance access are all influenced by the humidity strategy.
  2. It affects lifecycle costs. Passive systems require periodic buffer regeneration, while active systems incur ongoing servicing, monitoring, and component replacement.
  3. It determines conservation outcomes. An inappropriate strategy can place irreplaceable objects at risk.
  4. Retrofitting is costly and disruptive. Post-installation modifications often lead to compromises and increased expense.

A Balanced View: Designing for Performance and Practicality

The most effective solutions combine robust case engineering with an appropriate humidity control strategy. For many institutions, passively controlled, airtight cases offer the best balance between stability, reliability, and cost-effectiveness.

Mechanical systems should be reserved for situations where they are demonstrably necessary and where long-term maintenance can be guaranteed. Equally important is recognising when additional humidity control is unnecessary, avoiding avoidable complexity and cost.

Final Thoughts

Humidity control is one of the most influential—and least visible—factors in collection preservation. For specifiers, informed decision-making supports compliance with conservation guidance and responsible stewardship of heritage assets.

A display case is a protective environment. Humidity control is what makes that environment safe.

If you require assistance selecting an appropriate humidity control strategy or developing a display case specification, professional guidance can help ensure long-term conservation success.