Guest Author: Michael Bryant, Director of Sales - Mueller
When looking for the perfect way to seal your next product, the variety of potential gaskets on the market can be overwhelming. Chances are you’ve determined you need a gasket, but may not be sure of the material you need to use.
If you’re researching foam gaskets for your next electronics project, you’ve likely narrowed it down to the industry’s most prominent variants: open-cell and closed-cell foam. While they may look similar on the outside, both types of foam boast their own unique set of uses and properties. Below are some key difference that you should understand to help aid in making an informed decision.
How is Foam Made?
Before we get into the similarities and differences between open and closed-cell foam as gaskets, it is vital first to understand how these foam types are created.
Foams are created when a solid is heated and expanded with chemical injections, forming chemical gas-filled cell bubbles within the cells of the solid. Those bubbles then begin to expand, and whether or not the cells rupture determines the type of foam created.
For example, if the solid’s cells expand and rupture, the result is open-cell foam. If they expand but do not rupture, the result is a closed-cell foam. It is also worth noting that both types of foam can be created with varying degrees of thickness.
When asked about this process, our expert, Mike Bryant, compared it to baking a cake.
“You can take the same chemicals that are in plastic and add a blowing agent to them, that when heated creates bubbles. The bubbles are filled with gas, and they expand inside the plastic material, which creates foam … It is the same as baking a cake. It still has a pound of batter, but with all that air, it fluffed up and made a cake.”
While certainly not delicious, or edible like a cake, it’s a helpful analogy when thinking of how foam is created. Understanding the way foam is created is crucial to understanding the difference between open and closed-cell foams and their properties.
What is Open-Cell Foam?
Open-cell foam (polyurethane) is an incredibly versatile product. With its cells ruptured and open, it takes on a light, flexible, and very adaptable form. This type of foam has a very low compression set, which means that when compressed or weighed down by heavy items, it will return to its original form and thickness.
This can be incredibly useful for products that see heavy, repeated use, providing products with long service life. The open-cell foam also effectively seals out dust and air from products when compressed, making it an effective barrier from debris and other particles.
It is worth reiterating that open-cell foam can have its levels of thickness and openness adjusted. This means that certain open-celled foams can be more or less firm than others.
With its many uses, it’s no wonder that open-cell foam remains so popular in the manufacturing world. Open-cell foam serves many purposes, while also being very cost-effective.
What is Closed-Cell Foam?
Closed-cell foam is just as adaptable and well-suited to multiple tasks as open-cell foam, even though it does have key differences.
Since its cells are expanded but still intact, it has a higher compression set. This means that when compressed for long periods or with heavy items, it will not regain all of its original thickness. That being said, the closed-cell nature of this foam does lead to a more firm and sturdy gasket material.
Closed-cell foams are also highly water-resistant due to the closed-off nature of their cells. These qualities make this type of foam perfect for outdoor appliances or for any product that might be exposed to the elements.
With its tougher and overall more sturdy characteristics, closed-cell foam has plenty of uses in the electrical manufacturing space.
Comparing Open-Cell and Closed-Cell Foam Gaskets: Pros and Cons
Now that you’re a bit more familiar with both types of foam, it’s time to take a look at how they compare to one another. While somewhat interchangeable, there are some crucial elements of each that set them apart.
The flexible nature of open-cell foams are certainly a significant selling point, but it is not always suited to every task. For example, if you are using it as a gasket between two heavy pieces of sheet metal, the open-cell foam will get compressed between the two immediately and be rendered almost useless. On the other hand, the closed-cell foam will maintain a level of resistance when used as a gasket between heavier materials, making it the better choice for jobs requiring strength in materials.
Another critical element to consider when looking at open-cell and closed-cell foams as gaskets is their resistance to wear and tear, mainly from environmental factors. Both types of foam can be controlled to operate in similar temperatures, but water and air pose challenges.
Open-cell foams also have a strong resistance to dust and other debris but do not resist water very well. Closed-cell foams have a higher water-resistance as well as a strong dust resistance.
There are exceptions to this split, however. For example, open-cell foam is an excellent fit for appliances such as window unit air conditioners. The open nature of the foam allows for airflow but keeps out dust and debris. It allows moisture to pass through as well, but that is not a factor in this particular appliance.
Finally, each type of foam’s compression set is essential to consider. While open-cell foams have a low compression set and will regain its original shape after being compressed, the closed-cell foam will not return to its original thickness after being under similar conditions.
Industry expert Mike Bryant explained it best, saying, “If you take an open-cell piece of foam and a closed-cell piece of foam, both of them one inch thick, and you set them under a sofa cushion and sit on them for a month and then take them out, that open-cell foam is going to go right back to its original thickness. The closed-cell foam is going to have a very high level of compression set because you ruptured some of those cells.”
While many appliances feature closed-cell foam by default due to their strength and resistance to most elements, there is a place for open-cell foam in the electronics industry as well.
What About Crushed Foam?
Semi-closed cell foam, also known as crushed foam, is a hybrid of sorts that fits between open-cell and closed-cell foams. This type of foam is quickly becoming very popular in the industry, as it remains a formable material that also features some closed cells for environmental resistance.
This foam has become more prevalent in recent years for its adaptability. When a product moves between plastic and metal materials, you need a gasket that is flexible but firm, which is where crushed foam comes in. It excels at fitting irregular surfaces, as it is highly flexible while retaining its sealing qualities.
While this foam type might seem perfect for all uses, there is a catch. Crushed foam is less cost-effective than closed-cell foam, as it costs more for manufacturers to produce, meaning it costs more for you to purchase. This type of foam is made in two procedures: one to make it a closed-cell foam, and then another to crush a certain number of cells.
The Best Type of Foam Gasket to Use
Now that you are familiar with the two main types of foam for gasketing applications, it is time to decide which is best for your electronics needs.
If you are looking for a gasket that will retain its shape after constant use and work as an effective barrier to dust, debris, and wind, then an open-cell foam is a great place to start. If you need strength and moisture resistance, then a closed-cell foam will fit your needs. If you are looking for a happy medium between the two that is better suited for irregular surfaces, then crushed foam will be the perfect solution.
Ultimately, whatever foam you end up choosing for your next project will come down to what specifics you need to be catered to. Open-cell, closed-cell, and crushed foam all feature their own uses and characteristics as gaskets, different as the foams themselves might be. With all that in mind, the next time you need to make a buying decision for foam gaskets, you can utilize this guide to make the most informed, effective, and practical decision for your company.
For more information about Mueller Die Cut Solutions, visit: www.muellercustomcut.com