Polyurethane (PU) foam is an incredibly versatile material found in countless applications, from the soft cushioning of your sofa to the rigid insulation in building walls. Its adaptability stems from the ability to tailor its chemical structure and manufacturing process, resulting in a wide array of foam types with distinct properties. Understanding the classification of polyurethane foam is crucial whether you’re a manufacturer, contractor, designer, or consumer, ensuring you select the right material for a specific need.

Polyurethane foam is a solid polymeric foam based on polyurethane chemistry. As a specialist synthetic material with highly diverse applications, polyurethane foams are primarily used for thermal insulation and as a cushioning material in mattresses, upholstered furniture or as seating in vehicles. Its low density and thermal conductivity combined with its mechanical properties make them excellent thermal and sound insulators, as well as structural and comfort materials.

Polyurethane foam’s flammability depends on its chemical composition. To meet safety standards, manufacturers often add flame retardants. The material is classified under international fire safety standards such as:

• UL 94 (Underwriters Laboratories): Rates materials from HB (slow-burning) to V-0 (self-extinguishing within 10 seconds).
• ASTM E84: Measures surface burning characteristics for building materials.
• Euro class (EN 13501-1): Uses classifications like B-s1, d0 (low smoke and droplet production).

Closed-cell polyurethane foams generally outperform open-cell variants in fire resistance due to their compact structure. For example, rigid polyurethane foam used in insulation often achieves Euro class B ratings, making it suitable for commercial buildings. Always verify certifications with polyurethane foam roofing contractors to ensure compliance with local codes.

Reference: UL 94 Standards, ASTM E84

This is the German norm. In 2001 the European norm EN 13501-1 was introduced to examine and regulate the fire behaviors of building materials throughout Europe. It defines the material classes A to F:

• A: No contribution to fire (A1, A2)
• B: Very minor contribution to fire
• C: Limited contribution to fire
• D: Acceptable contribution to fire
• E: Acceptable fire behaviors
• F: No effect established

This classification relates to whether the tiny cells that make up the foam structure are interconnected (open cell) or largely isolated (closed cell).

• Open-Cell Polyurethane Foam: In this type, the cells are deliberately left open and interconnected. This structure allows air to move freely within the foam.
  • Properties: Open-cell foam is typically softer, less dense, and more flexible. It is a good acoustic insulator, absorbing sound waves as they pass through the interconnected pores. It has a lower compressive strength and offers a lower R-value (thermal resistance) per inch compared to closed-cell foam because air can still move within the structure, facilitating convection. It is permeable to vapor.
  • Applications: Common uses include furniture cushioning, bedding, packaging, soundproofing materials, and some forms of spray foam insulation where air permeability and flexibility are desired over maximum thermal resistance or a vapor barrier.
• Closed-Cell Polyurethane Foam: Here, the blowing process is controlled so that the cells remain largely encapsulated and distinct, like tiny balloons. The blowing agent gas (which often has lower thermal conductivity than air) is trapped within these cells.
  • Properties: Closed-cell foam is significantly more rigid, dense, and structurally stronger than open-cell foam. The trapped gas provides higher thermal resistance, resulting in a much higher R-value per inch, making it an excellent thermal insulator. It acts as a strong air barrier and a vapor barrier, resisting moisture penetration.
  • Applications: Widely used in rigid insulation panels, spray foam insulation for walls and roofs, flotation devices, structural components (like composite cores), and in applications requiring high strength and resistance to water or vapor.

The choice between open and closed cell foam often depends directly on the desired balance of insulation value, structural support, cost, and moisture/air barrier properties.

Donyan pu foam A1

Donyan pu foam A2

Donyan pu foam A3

Donyan pu foam A4

Polyurethane foams are also broadly categorized based on their mechanical behavior – whether they are flexible and bouncy or rigid and structural.

• Flexible Polyurethane Foam: This is the type most people interact with daily. It is designed to be soft, resilient, and return to its original shape after compression. Chemistry is optimized for elasticity.
  • Properties: High elasticity, low compression set (doesn’t stay compressed), good shock absorption, comfortable feel. Density can vary widely, affecting firmness and durability.
  • Applications: Upholstery for furniture and automotive seating, mattresses and pillows, carpet underlay, protective packaging, sponges, and some textile laminates. Flexible foam is often open-cell, though not exclusively.
• Rigid Polyurethane Foam: Unlike its flexible counterpart, rigid foam is designed for strength, insulation, and structural integrity. Its polymer matrix is more cross-linked, making it less elastic.
  • Properties: High compressive strength, excellent thermal insulation (high R-value), lightweight, good dimensional stability, often acts as an air and vapor barrier (especially closed-cell rigid foam). It does not easily deform under load.
  • Applications: Building insulation (spray foam, panels like PIR – Polyisocyanurate, a modified PU), refrigeration, pipe insulation, roofing insulation, flotation, and structural composites. Rigid foam is almost always closed cell.

The distinction between flexible and rigid is primarily determined by the types of polyols and isocyanates used in the formulation and the degree of cross-linking in the polymer structure.

Donyan Polyurethane Foam A1

Polyurethane Foam pu foam A1

 

• High Intensity
• Pre-expansion
• High Elasticity
• Smell Cell
• 28 Running Meters

Donyan Polyurethane Foam A2

Polyurethane Foam pu foam A2

 

• High Hardness
• Easy & Convenient

Understanding these classifications directly informs material selection for practical problems:

• High-Performance Insulation: For maximum thermal resistance and an air/vapor barrier, rigid, closed-cell spray foam or panels are typically chosen, considering density for strength and R-value requirements. This is where polyurethane foam roofing contractors specialize, applying rigid SPF.
• Comfortable Furniture: Flexible open-cell slab stock or molded foam is selected based on desired firmness, durability (linked to density), and shape requirements.
• Sound Control: Open-cell flexible foams are preferred for their sound-absorbing properties.
• Structural Components: High-density rigid molded or poured foams are used where strength and lightweight are needed.

Polyurethane foam’s remarkable versatility is a direct result of its ability to be engineered into different forms with a wide range of properties. Classifying PU foam by its fundamental structure (open vs. closed cell), flexibility (flexible vs. rigid), manufacturing method (molded, sprayed, slab stock), and key properties like density and fire resistance provides a clear framework for understanding this complex material. By grasping these classifications, professionals and consumers alike can navigate the vast landscape of polyurethane foams and select the ideal type for their specific project or product.