In this first teshuva in this collection, the Netziv deals with a statement of the Magen Avraham who writes that one can put wool tzitzit on a linen tallit (in seeming violation of the laws of shatnez) if the corners of the tallit have leather patches on them. He initially raises two questions on this position. First, whether or not leather serves as a barrier vis-a-vis the laws of shatnez is actually a debate in the mishna in Kilayim. Second, there is a view that the tzitzit have to be made out of the same material as the corner from which they hang, and if that corner is made out of leather then there would be no obligation to have tzitzit there in the first place.
The Netziv then adduces a gemara in Yevamot which proves from a pasuk that shatnez is not a problem when it comes to tzitzit. However, he responds that the pasuk should not be needed if the leather patch can serve as an effective barrier. In other words, which is the true reason why this set-up should be permitted?
The Netziv spends some time on whether having or not having techeilet makes a difference (he says it does not), and whether this would be considered to be a situation of מצוה הבאה בעבירה. In the end, he concludes that there is no need to make a decree restricting one from making such a tallit, since if someone takes the time and effort to add the leather patches the chances are that we no longer have to worry about shatnez in that case.