Should viscoelastic foams have an open cell structure?
Choosing between an open or closed cell structure will depend on the desired application.
Cell open or closed?
Closed cell foam has a more homogeneous structure, lower thermal conductivity and lower absorption capacity to water, moisture, etc. when compared to open cell foams. There are thus industries that use closed cell foams in response to specific needs.
The cosmetics industry, for example, benefits from the low absorption capacity of closed cell foams to make foundation applicators, so that they spread the product instead of absorbing it.
In the automotive industry, car seats are traditionally made of closed cell and molded foam, as it has lower production costs, allows series and accurate reproduction of the shape of the model, which is more variable in open cell foams (due to the type of production technique and machine cutting).
If impermeability and insulation are intended, open cell foams will be at a disadvantage, as they allow air, heat, sound, and water to pass through them more easily. Therefore, in the construction sector, closed cell foams are more common.
Open cell foams have higher porosity. That is, they allow the passage of a greater flow of air, heat, and humidity. At Eurospuma, we privilege these characteristics, because in our traditional markets – bedding and furniture – products are in direct contact with the body, requiring the greatest possible hygiene and thermal comfort.
If the mattress system is well built (including the mattress cover and even the canapé), open cell foams maximize user comfort by preventing the accumulation of heat and moisture from the body while sleeping. Thus, all the conditions for a good night's rest are met!
The compression set of open cell foams is generally lower than that of closed cell foams, which means that their ability to recover after compression is greater. Some closed cell foams used in bedding and furniture do not fully recover their initial dimensions after intense and lasting compression.
Viscoelastic foams must have an open cell?
Viscoelastic foam is formulated to absorb more pressure, molding itself to any shape and body weight. It slowly recuperates its original format after compression which is why it is often called "memory foam". Viscoelastic foam also reacts to temperature changes - it gets harder with cold and softer with heat. Depending on formulation and application, its cellular structure can range from very open to almost closed.
Traditionally, viscoelastic foams are more closed than other types of foam, due to its raw materials and production method, but also because they have a smaller cell size. These foams are used in applications where comfort is most valued and the circulation of air and humidity are essential to maintain not only thermal comfort, but also hygiene of bedding products. Thus, a more closed viscoelastic foam is at a great disadvantage compared to a more open viscoelastic foam.
Given the type of polymeric and cellular structure it has, an open viscoelastic foam’s compression set is among the lowest (and most favorable) values across all types of foam.
Our portfolio offers a set of open cell solutions, based on COOLFLOW technology, which aims to improve the air circulation of foams, namely viscoelastic ones. There is also the possibility of integrating metallic or organic particles into foam, which maximize the body's heat and moisture dissipation capacity, such as COOLGRAPH, TITANIUM and CUPRUM technologies.
Players in the bedding industry who do not choose open cell foams, for reasons of apparent cost, end up using "refreshing" covers and other materials, which try to "cover up" the air circulation limitations of closed cell foams. Many pillow producers choose to use closed cell foams because the waste is minimal compared to open-cell foam, where the block needs to be cut into shape. Yet, these producers end up cutting holes into the foam, to try to create air circulation and maintain thermal comfort. In the end, although closed cell foams are more competitive, they lack the mandatory air circulation characteristics that open cell foams offer. What was initially cheap, turns out to be expensive!
Overall, our 56 years of experience proved to us that open cell viscoelastic foams are the most suitable solution for the bedding and furniture industry.