We have a half wall that divides the dining room from the steps
leading down to the basement. The problem is that on the corner of the
wall (which is rounded), the paint has peeled off in large chunks
exposing what looks to be plastic underneath. Is it plastic? Would
the entire wall be constructed of this? What can I use to patch this
up?
And, for my future reference, is there an easy way to maybe even
cap off the wall with a nice looking wooden cap or something?

Thanks!