Mad about Science: Foam

By Brenden Bobby
Reader Staff

Nothing beats a lazy morning laying on the bed, thumbing through your phone and enjoying the comfort of sinking into a foam mattress topper. Ever wondered how they make that soft, cushy foam cover? What is it made out of and how does it get its shape?

Manufactured foam comes in a lot of varieties. There may be as many as three different types of foam used in your mattress alone.

Mattresses will often use one or multiple types of foam: latex, memory foam and polyurethane. Polyurethane is the most common and cheapest form of foam used in beds. It is derived from petroleum-based chemicals called diisocyanates that are mixed with sugar alcohols called polyols. This mixing creates polyurethane; and, when air is introduced into the mixture, it becomes trapped to create the aerated structure of the foam. Poly-foam is then cut into precise sizes and added to beds or simply rolled up and sold as foam mattress toppers.

Memory foam is polyurethane foam with additional chemicals added to give it the unique qualities we know and love, such as retaining an indentation for a prolonged period of time. Memory foam generally has greater longevity than regular polyurethane foam, but the “squishy” quality of memory foam can be uncomfortable to some that prefer a firmer mattress topper and more support.

Producing latex foam requires a different process from polyurethane — using organic rubber compounds from rubber trees and putting it through a process called vulcanization. 

I know what you’re thinking and, no, the foam isn’t told to “live long and prosper.” The vulcanization process is essentially applying heat and pressure to the rubber, in addition to some other chemicals to rapidly cure and transform it into the foam structure we recognize. 

The rubber is placed in a container with sulfur and a number of other activator chemicals and then heated to 400 degrees Fahrenheit. At these temperatures, the sulfur begins to react with the rubber molecules to create cross-links that increase its durability and longevity. This is a common process when making foam, so the term “vulcanization” may come up frequently on this page.

Outside of the bedroom, foam appears virtually everywhere in our lives. Ethylene vinyl acetate, or EVA foam, appears commonly in gyms, sporting complexes and in cosplay. Its most recognizable form is the black gym mats and floor covering with edges cut to look like puzzle pieces — these interlock and create a large, low-cost surface area. It is produced by mixing ethylene and vinyl acetate in a vat and then squishing the product down to produce a sheet. Following that, it’s vulcanized like latex foam and enters secondary processing. 

Secondary processing for EVA foam can take many forms, depending on the desired final shape. If it’s being made into modular floor mats, it is pressed by a die and cutter that imprints a texture onto its surface and creates the interlocking edge pieces by exerting immense pressure.

EVA foam is commonly used for cosplay props due to its rubber-like elasticity and lightweight nature. It also holds a texture well and is easy to process at home with basic household tools, giving crafters the ability to create hyper-realistic armor that’s lightweight and easy to paint or repair.

Expanded polystyrene, or EPS foam, is perhaps the most common form of foam we see in our everyday lives. This is regularly used to insulate houses, but can also be found protecting electronics and other fragile items during shipping as a white flaky foam that gets everywhere. You’ve probably heard this referred to as styrofoam.

EPS foam is produced by creating polystyrene pellets that are mixed with an expanding gas. These pellets are fed into a machine that heats them with steam to both melt the plastic and expand the gas to create foam. Polystyrene is also used in many other applications — my favorite being tabletop miniatures — however, high-impact polystyrene used in miniature creation does not contain expanding gas compounds.

EPS foam is formed into a brick mold to create a uniform rectangular shape. In many cases, this is a continuous process where a long line of foam is pressed down a conveyor and cut by a rolling guillotine that matches the pace of the line in order to produce smooth and uniform cuts. The chemical composition of the foam is altered prior to its heating, depending on the final application. Insulation foam will often be denser and less flaky than packing foam.

Bonus fact: Larval mealworm beetles will actually consume polystyrene as a food source. While this process is extremely slow, it doesn’t appear to have any detrimental effects on the worms or the creatures that eat the worms. Mealworms are very easy to raise and make a great treat for backyard poultry like chickens, turkeys and guineafowl.

The process of producing cans of expanding foam is similar to the polyurethane foam used in mattresses by employing an isoalcohol and polyol, along with an aerating compound that shoots the chemicals from the can and traps air inside to create a foamy texture. The chemicals in this stuff are particularly nasty when exposed to heat, so if you ever need to shape or mold it with a hot knife, it’s imperative that you have adequate respiratory protection.

None of this foam is the stuff you want on your peppermint mocha, but the principle is similar to whipped cream. Trap air inside of a semisolid structure and voila! Foam at your fingertips, on your nose and in your beard.

Stay curious, 7B.