There are primarily two different types of foam, with a number of subsets under these two categories.
Polyurethane foam is a softer, open cell foam that allows air and liquid to penetrate through the foam. Polyethylene foam is a more firm closed cell foam that is more dense and rigid.
Both foams are good for shock absorption and thermal insulation. Polyethylene foams are typically more chemically inert and will also resist water and bacteria growth because of their closed cell structure. Polyurethane foams come in a more wide variety of styles and formulations allowing the user to pick a product suited for the desired end-use.
Foam is generally categorized by its density, which is referred to in pounds per cubic foot. For example, 1.9#, 2#, 4#, etc.
Polyurethane (Open Cell)
- Polyester (ester) Foam – This is a type of polyurethane foam that is very widely used. It can have fire ratings, color added, anti-static coatings, and other factors that make it universal. Polyester foam is ideal for sealing as it naturally prohibits air flow. In addition, polyester foam has greater abrasion and cut resistance than other types of polyurethane foam.
- Filter Foam – this is a subset of polyester foam where the foam is needled or has pockets inserted through the foam. This foam is used for air or liquid filtration. Filter foam is categorized by the number of pores per inch or PPI. For example, 100 PPI foam has 100 holes per inch.
- Polyether – this is the other type of polyurethane foam (a sister to ester). This foam tends to have a more open structure and will typically have less tensile strength than ester foam.
- Poron – Poron is a polyurethane foam made by Rogers Corp that is used specifically for gasketing. It is widely used across many industries as it is durable and allows for long-term performance. In addition, Poron is flame retardant, has good chemical resistance and comes in a variety of densities.
Polyethylene (Closed Cell)
- Expanded Polyethylene Foam – This type of foam is rather strong and resilient with excellent resistance to chemicals and grease. This foam is also mildew and bacteria resistant. It is commonly used for vibration resistance as well as a range of packaging applications.
- Cross-Linked Polyethylene Foam – This foam has been chemically crosslinked. This creates a uniform finish and has better physical and chemical properties than conventional polyethylene foam. This type of foam has excellent memory due to the cross-linked structure. It also carries excellent strength and resistance to chemicals and grease. A common trade name of cross-linked polyethylene foam is Volara.