Another foam acronym that is good to have an understanding of is EPO ( Expanded Poly Opalene). This is important for beginning hobbyists to learn because this foam is starting to dominate the market for foam model R/C aircraft.
When compared to models that use EPS (Expanded Poly Styrene), EPO foam has larger cells that have a heavier density. Another difference from EPS foam is that EPO is flexible and is prone to bending, especially if you were to leave your plane out in the heat. This is why aircraft made of this type of foam will have added reinforcement such as carbon rods.
Although EPO tends to be a heavier foam than EPS (especially when adding the necessary reinforcement) there are many benefits that come along with having a model built from this type of foam. One positive aspect is that when dealing with EPO models, you can use regular CA glue that most everyone has rather than needing a special foam safe glue.
EPO also tends to be a very durable foam that has the ability to act like a sponge when it receives a dent as it will expand back out. Although it tends to be a heavier foam, its durability far outweighs the weight. Also this type of foam has been refined so it can have an excellent looking finish to the molded parts.