: Polyurethane glues will only foam when they are allowed to expand
: unrestrained. This same characteristic helps force the glue into the grain
: of the wood, making for a strong joint.

But only on joints with endgrain. No glue can force itself through edge or face grain. This is why there is really no difference between PU and Titebond glues used in gluing edge to face, edge to edge or face to face. With proper joint prep, both glues will make those joints stronger than the wood itself. Anytime you glue end to any other kind of grain, you have a weak joint regardless of what glue you use unless you strengthen it in some way, such as scarfing, common in boat building, or doweling or biscuits or other types of joinery. Yes PU glue is supposed to be stronger in end to any grain type joints, but these joints, even when using PU glue, are still weaker joints than the wood itself. One thing PU has going for it is that it may be as waterproof as epoxy (I have not seen anything comparing PU to epoxy "waterproofness", yet) without the hassle of mixing before applying, like epoxy requires. Other than that, I really do not see much advantage in PU glues for most *woodworkers* unless they make a lot of outdoor furniture. For boatbuilders, however, I believe the issue is still a bit muddy, yet. If the glue is goint to be protected by epoxy or epoxy-FG finish, then Titebond should work fine, for joints that will only be protected with paint and/or varnish, PU might be a better choice, IMHO. For "unprotected" joints (like many SOF's frames, note: I do not consider an oil finish, like boiled linseed oil or tung oil, to be any kind of protection), however, I do not know if I'd trust PU, I'd lean towards using epoxy which has a successful track record.

Paul