I'm not familiar with Tyvek Commercial, so I can't give a direct comparison. But for a rainscreen application, our topic here, Vaproshield is superior. I like it because it is designed to be used as an underlayment for a rainscreen application. So, they kept a few specifics in mind when designing it. 1) It's self sealing 2) It's available in black 3) It is rated for up to 8 months (!) exposure before covering. 4) It's ability to quickly release any moisture trapped behind it (on the house side) is far superior to Tyvek. Vaproshield also comes in these preformed corners that make your window installations real tight. 

I've seen too many houses with the Tyvek sitting out in the sun, getting beat up and basically disintegrating. It's just not worth the chance, in my opinion. As far as cost, I can't remember off the top of my head, but it was slightly more than Tyvek, but I was fine with that when figuring the performance plusses.

Jason - I wish you would post here and let us know what happened!

  -R.

Hey Guys sorry for the lack of response. I have been in the process of moving things into our house under our temporary CO and still trying to finish up the interiors.

We ended up not using a rain screen system all together as a result of several things. 1. I wasn't confident that the SIPs panels could hold the weight of the hardiboard. 2. the city was going to require us to go back and have more engineering/design drawings done to prove it  and those bills had already climbed well above what we wanted to spend. 3. SIPs panels actually breath on their own so the rain screen was a bit of a redundancy. We ended up putting the hardiboard over top of a house wrap materials that was specifically engineered for SIPs panels. I still think that the rain screen system is one of the best solutions out there for house exterior and additionally I love the way they look. If we would have stick framed the house I would have used it and put on the Vaproshield which from my research seems like the best option and it's affordable.

Jason