Open-cell vs. Closed-cell Foam
Foam tapes with or without adhesives play important roles as gap-fillers in providing dampening, sealing and protecting properties in automotive, building and construction, aerospace or transportation applications. For many, foam is just foam but there are significant differences.
Although open-cell foam and closed-cell foam may have similar appearances on a first look, their different construction requires them to be treated as different product types because their properties and performance can be completely different. It would be more like comparing apples to pineapples just because their names are close.
Therefore, understanding the differences between open-, closed-cell and even micro-cellular foam designs and their specific strengths and weaknesses is essential to choose the right solution for your application, save time and money and to maximize outcome, value and benefit for you and your customers. Or, to express it with the above comparison, to avoid that the supposed apple pie tastes significantly different because a similar-sounding fruit was chosen.
Every foam consists of numerous gas pockets or pores in different sizes. Besides the material formulation of the foam, these pores and their structure influence suitability and features for your applications. In open-cell foams, reactions during the production process cause pockets of gas to expand and break, leaving them ‘open’ and thus allow air to occupy the space within.
Its porous nature and air infiltration provide good thermal and acoustic insulation properties and its high expansion capability, conformability and durability make it a good choice for sealing and dampening where liquid, water or water vapor resistance is not needed. The water absorption properties of open-cell foams can also be required, depending on the application.
The low-density design of open-cell foam typically is lightweight, soft and easily comes back to its original shape after compression. Its minor compression resistance results in the reduction of this ‘spring’ effect over time. Open-cell foams are often based on Polyurethane, PVC or EPDM and perform as cost-effective solutions for absorption, dampening and insulation applications where moisture, air and water permeability are required or tolerated.
Closed-cell foam is a strong, flexible material where internal pores are intact and filled with gas. The pores sit closely together but are not interconnected. Depending on the gas within the pores, it can be highly efficient in increasing the insulation capability of the foam.
Closed-cell foams are usually of higher weight due to their medium-to-high density, which helps to keep the pores in place and provide good sealing properties against water, vapor, liquids, air, dust or other environmental influences.
Especially when designed with silicone materials, closed-cell foams provide excellent thermal insulation properties even under extreme conditions and high-end applications, such as EV battery packs. By matching materials, gas, thickness or density, closed-cell foams can be optimized for different interior or exterior sealing, insulation, cushioning, padding and gasketing applications.
Often made from polyethylene, polystyrene, rubber, silicones to polypropylene, the costs for closed-cell foams are typically higher than open-cell foams and best for high-end applications in demanding markets like automotive, EV, industrial, construction or aerospace.
Micro-cellular foams are special closed-cell foams where the pores are reduced to minimal size. These fine cell sizes result in a high-density product with excellent insulation characteristics. Depending on the gas, the foam’s density can be between 5% and 99% of the pre-processed plastic, which has a big influence on behavior and performance.
Understanding the differences, strengths, weaknesses and general applications mentioned in this overview is a good start in selecting the right material for your needs. Of course, there’s a multitude of variations available and each foam type can also be modified to meet more specific requirements like insulation, sealing, fire-resistance or flame-retardance, densities, thicknesses or weight.
But next time you have foam materials in hand, this overview should help you quickly identify its nature and give first ideas of its use. And after all this talk about apples, pineapples and pie, stay hungry for other interesting topics in our blog and maybe enjoy a little snack in the meantime.