It is not uncommon for budding hobbyists to be afraid to ask questions that they feel they should know. This can be especially true when you are speaking to experienced hobbyists who can at times seem to be speaking their own language. You will often hear acronyms used as frequently as actual words and when you are in a full discussion or listening in, it may be difficult to even know where to begin asking questions. One of the acronyms that could be useful to know, especially in regards to your foam R/C aircraft, is EPS.
EPS stands for expanded poly styrene. This type of foam is much like your beer cooler type of foam. It is extremely light weight and is great for producing a nice surface for moldings in things like the wings and fuselage. The beads are very small and pack together tight to produce a nice flush looking surface. The downside to this type of foam, however, is that you can’t just use a regular CA type of glue. EPS requires a special, foam safe glue. Also, it is very prone to dents and dings, or “hangar rash” as many hobbyists call it. So, on the one hand, you have a foam that is not very resilient or durable, but on the other hand, this foam is great for low weight impact on the model, along with providing a nice overall look.