Wayne, thanks for the very detailed answer. I will take your advice and use R13. I assume that once the R13 is stapled in place you don't have to been concerned about any glass fibers drifting out of the port hole and breathing them? Sorry if this question is too dumb.By the way, I purchased your kit (thermionic 3) and I'm glad I did. Instructions are very clear. Construction is not that difficult, even for a novice. Thanks.