We've started drywalling our new house and I have to seal all the windows and doors. We used SIPS, Sprayfoam and triple pane windows so I don't want to cheap out here. I went and bought foam for windows and doors as it says right on the can and was what was suggested by the sales rep but now when I spray it the wood framed doors are fine but all the vinyl window jambs are bowing in. Granted some came from the manufacturer with a slight bow. I've been going back cutting it all out, luckily I only did about 12 of the 30 windows to try it again.

 I made some wood bracing for a couple to try it out and it seemed to work but seems like a lot of extra work not to mention a waste of wood as they are all different sizes. So, am I putting too much in as I try to fill the whole 6 1/2" deep jamb or is it normal to have to brace them. I thought maybe I could just shoot a couple of inches at a time at random places around the window and let it dry. Any other ideas or guidance would be appreciated.

Thanks,
Sean

Sounds like you are you using "big" gap filler,  you need a low expanding foam specific for doors and windows

sgo, did you get the foam in the pressure cans with a straw from big blue or big orange, or something similar? If so, do yourself a favor and find a contractor's supply house, or maybe even a tool supply house and buy a foam gun. Then get the foam in cans made to be dispensed with the gun. One of those cans will yield as much foam as maybe ten or more cans of the Great Stuff variety. The non-expanding, i.e., no expansion pressure, commercial foam will be safe for your doors and windows, and will fill big gaps. I used many cans of the stuff while building my house and never saw it push anything apart. It just leaks out the nearest hole, or simply sets up in the space available.

A couple of sliding clamps with the jaws reverse make a good temporary brace. No waste either

We also have heavy triple pane windows on our new house. The window manufacturer recommends 3/8" expanding foam on each side of the windows for a good thermal break, but the contractor is thinking of 1/2" -- but would that make the windows unstable? Another contractor said he uses 1"! What is standard out there in the green industry?
Thanks,
...Terry

Rough openings are 3/4" larger than frame size so you get 3/8" all around in most windows. The windows shouldn't be suspended in the opening by the fin, they need to be shimmed so to answer your fear of instability, no they will not be unstable because they are shimmed. If he was just going to hang the windows by the fin and not shim get a different guy.
And in rough opening take into account your sill pan and flashing material like vycor and beveled cedar if you use that and add that to the height. Those layers add up quickly.

1/2" on each side is nothing to get excited about but 1" on each side and you wouldn't be able to nail a flanged window in because the opening would be too large. So I'm not sure what that guy's doing, sounds a bit hackey.

+1

Hanging windows without proper shimming is a no-no.

Foam is fine is the proper foam and technique is used.