When defining a radiation for a surface ("wall"), of course emissivity and absorption coefficients are required. Many materials datasheets don't offer this data, particularly absorption. What is commonly done for these cases? Educated guess? Let's say for example a translucent plastic such as Ultem. (I guess I'll say the obvious, radiation from a relatively low temp material such as this is probably negligible, but anyway...).
And is specularity coefficient important? What's an example of how this is used when solving for radiation heat transfer?