Structural Insulated Panels - The Facts

Building an Energy Efficient Structure:

Different components formulate the construction of an energy efficient structure: foundation, exterior walls, floors, roofs, insulation, doors, windows, lighting and heating systems all play important roles in the way in which energy is consumed. Critically, the most important element of any energy efficient structure is the design of the building envelope (foundation, floor, walls and roof). It is renowned across the construction industry that many techniques are deployed by architects, designers and building contractors in designing and constructing the building envelope. Dependent on the design, some will perform well, though they can be quite expensive to construct and potentially require many years before bringing a form of payback into fruition. Other designs are cheap to formulate and construct, but compromise on performance and do not deliver as promised. The only design that provides the industry leading quality of comfort, in conjunction with reducing energy consumption to provide the best possible energy savings, is utilising a design that incorporates the Kingspan TEK® Building System, a composite building product. The Kingspan TEK® Building System comprises 142 mm or 172 mm thick structural insulated panels (SIPs) with a high-performance polyurethane (PUR) insulation core, sandwiched between two layers of Oriented Strand Board type 3 (OSB/3).

PUR Structural Insulated Panels or EPS Structural Insulated Panels?

When researching about SIPs there are two types of foam that form the insulative layer within the panel during manufacture, Polyurethane (PUR) and Expanded Polystyrene (EPS). The Kingspan TEK® Building System is the only SIPs system manufactured in the UK utilising PUR insulation, in comparison to competitor systems that will manufacture using an EPS core. You will find an abundance of web articles that are promoting expanded polystyrene over polyurethane SIPs but this statistic is not relative: quantity is not equal to quality.

Polyurethane is a relatively new product in the construction realm, having been around in industry for around 35 years. The fact is that polyurethane was produced to replace the pitfalls of expanded polystyrene. A common misconception in the industry is that some companies will promote their products as ‘SIPs’, when in fact they are actually offering a closed panel timber frame, with foam-board inserts between the studs. The video below provides a visualisation into how the Kingspan TEK® Building System is manufactured in the UK, demonstrating the correct way a Structural Insulated Panel should be formed:

How are structural insulated panels made?

How are structural insulated panels made?

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The Difference Between PUR SIPs vs EPS SIPs

The technology, structural performance and thermal performance between a PUR SIP against an EPS SIP is the same as comparing chalk and cheese. Below we venture into the facts deeper and outline in detail the key differences between Polyurethane (PUR) and Expanded Polystyrene (EPS) SIPs. 


The biggest difference between Polyurethane and EPS lies in the way the panels are manufactured. Both products use OSB for covering both sides of their insulative layer, but this is where any similarities end. In the bonding process of the foam, the actual polyurethane is used as the bonding agent to the OSB faces itself. Polyurethane is one of the best glues in the construction industry today. Manufacturers of plywood and OSB use polyurethane to bond their products together. This method of adhesion provides both the strongest bond in the industry and excellent R values. On the other hand, EPS panels use glue spread on both sides of the OSB. The OSB is then matched together with the EPS core and mechanically held in place and under pressure until the glue is dried.

Curing Process

During the manufacture of PUR SIPs, the chemical reaction created after injecting the polyurethane’s two component mixture causes the foam to expand over 50 times its volume in less than 10 seconds and is tack free in under 2 minutes. The foam generates pressures of 15 psi and temperatures of 180°C, that impregnate into the OSB fibres. This results in a closed cell structural insulated foam panel, offering immense strength (6x stronger than conventional stick framing). Once cured it becomes a thermoset plastic that will not change. In comparison, EPS SIPs glued panels are placed into a press or vacuum bag and held until the glue has set. It is not uncommon to find EPS SIPs that are not plumb/square across its edges. EPS SIPs are only as strong as its weakest connection – that being the glue bond of the OSB to the EPS beadboard. This can lead to a high risk of delamination of the panel.

Chemical Resistance

Polyurethane is resistant to petrochemicals, most counter chemicals and other common household chemicals. EPS violently reacts with petroleum-based products, for example PL 400 and liquid nail will burn straight through EPS. In addition, EPS is highly susceptible to oil and solvents and will melt upon contact with each other.

Moisture Resistance

Polyurethane is impervious to water absorption and as such maintains a constant R value. On the other hand, the open celled structure of an EPS core, provides an avenue for water to penetrate and be absorbed by the insulation up to 4.3% in volume. Any form of penetration through the vapour barrier and OSB skins accommodates for moisture laden vapours to be infused and absorbed by the panel. In time, these vapour pockets will reach dew point and water will become trapped. When the EPS core and OSB skins become saturated with water, this will detrimentally affect the structural properties and performance of the panel.


Polyurethane as a thermal-set plastic does not melt, in stark contrast to polystyrene. The fact is that polyurethane, when exposed to a continuous open flame, will remain mostly undamaged by heat until temperatures reach around 400°C, where at this point the material begins to char. Polystyrene is not a thermal-set plastic and will melt at temperatures in the 100°C -150°C range. Beyond this range, the Polystyrene can become a fuel to the fire. Polyurethane has the superior advantage.

Noise Abatement

As polyurethane shares some of the characteristics of rubber, it is useful in achieving mechanical sound reduction, for example machine gears made from this polymer make a lot less noise.


Building with the Kingspan TEK® Building System vs Conventional Stick Framing

When comparing the life cycle energy consumption of a building constructed using SIPs verses stick framing, the fuel consumption benefits of using PUR SIPs far exceeds the benefits of stick framing and those of other competing construction methods. Additionally, when comparing the construction methods of SIPs with stick framing, one should consider all the cost-effective benefits SIPs provides such as:

  • Reduced construction time (consequently reducing the cost of construction time on-site)

  • Reduced labour costs

  • Fewer sub-contractors/follow on trades to schedule on-site

  • Reduced on-site waste

When you take into consideration all these costs, SIP construction can cost around the same as stick framing (sometimes be even more cost effective). In the current climate where gas and energy bills have recently experienced a sharp increase and will continue to increase year after year, it only makes practical sense to build with the Kingspan TEK® building System.

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