Insulating Glass FAQs

Insulating glass units are two or more panes of glass held together by a spacer around the perimeter and typically filled with an inert gas to reduce thermal transfer.

An insulating glass spacer is a key part of an insulating glass unit (IGU). It keeps the glass panes apart, holds a drying agent (desiccant), and helps seal in insulating gas while keeping moisture out.

There are several types of spacers, each with different materials and benefits:

• Aluminum Box Spacers – metal tube containing desiccant beads.
• Stainless Steel Box Spacers – metal tube containing desiccant beads.
• U-channel spacers – metal channel with desiccant matrix inside.
• Thermoplastic Spacers (TPS) - Flexible thermoplastic material with integrated desiccant.
• Foam Spacers – foamed material with integrated desiccant and a vapor barrier film.
• Hybrid or Composite Spacers - Combination of metal and plastic (e.g., stainless steel + polymer) - filled with desiccant.

• Maintains separation between glass panes.
• Contains desiccants to manage moisture.
• Provides a base for edge sealants.
• Acts as a gas and moisture barrier.
• Enhances durability and seal longevity.

Glass with low-E coatings, inert gas, and high-quality sealants, reduce thermal bridging and temperature transfer through the unit —helping meet stringent energy codes. Adding warm edge spacers further reduces heat transfer on the perimeter of the unit.

A warm edge spacer has lower thermal conductivity than a traditional aluminum box spacer and therefore reduces thermal bridging around the glass perimeter. H.B. Fuller Ködispace™ 4SG is a leading warm edge spacer system made from reactive thermoplastic materials that deliver superior insulation and edge seal integrity.

• Lower Heat Transfer: Increases window energy efficiency.
• Energy Savings: Helps reduce HVAC demand.
• Condensation Resistance: Keeps interior glass edges warmer.
• Comfort Improvement: Reduces drafts near glass.
• Long-Term Flexibility: Adapts to seasonal temperature swings.

A sealant used to seal the edges of two or more panes of glass in an insulated glass unit (IGU) to prevent moisture and air from penetrating the space between the glass layers and maintain the unit's insulating properties. It also helps to bond the glass and spacer components together. 

The primary sealant resists moisture vapor ingress and prevents insulating gas from escaping. The primary sealant must have resistance to UV and heat degradation and maintain a seal during temperature extremes.

The secondary provides structural support.  It bonds the glass panes and spacer together to form a strong, unified unit and acts as a barrier to moisture and vapor penetration.  It also helps maintain the mechanical stability of the IGU, especially under thermal expansion, wind loads, and handling stresses.

H.B. Fuller Ködispace™ 4SG is a thermoplastic spacer that combines the spacer, desiccant, and primary sealant.  It bonds directly to the glass panes to create a tight seal. This technology simplifies production, strengthens IGU durability, and improves energy ratings. The flexible, permanently elastic formulation supports automated manufacturing and curved designs.

A thermoplastic spacer is polymer-based, offering low conductivity and flexibility.  Ködispace™ 4SG sets the industry benchmark for performance and adaptability in both standard and custom-shaped IGUs.

Structural glazing uses silicone sealants to bond glass directly to the building frame, without visible mechanical supports.

• Clean Appearance: Frameless look with hidden supports.
• Flexible Design: Supports two-sided, four-sided, or total vision systems.
• Material Compatibility: Pairs with laminated or tempered safety glass.
• High Performance: Provides insulation, weatherproofing, and UV stability.
• Ideal for use in high-rise facades, airports, and commercial glass walls.

Silicone adheres glass to the aluminum frame to manage structural loads, building movement, and weather exposure.  It requires testing for long-term performance in demanding environments.