As many have noted, I can't find splines for my BC install. I found some poplar that is 1/2" thick and fits perfectly when cut on the table saw. Will this wood be acceptable or is it too soft for a spline?

If I use hardwood, I would have to plane it down or cut each spline to width after they have been cut to fit inside the groove. I would rather avoid this so am considering the poplar.

Also, would pine be too soft or would plywood work? It seems the cut would leave the plys weak as they would be aligned parallel to the groove.

Once I get the splines glued in, I would like to avoid face nailing, but I think the staples may tear up the spline (will use scraps to support as Gary suggested on other posts). Is it better to use the finish nailer or drill and hand nail?

Thanks in advance (I got started this weekend and have 2 rooms almost completed - wouldn't have gotten this far without all your help!)

the splines that are available commercially are mixed hardwoods often poplar. I say go for it.