To say they're atypical in a world of rock 'n' roll excess would be something of an understatement.

Formed as a side-project for members of The Operation in 2001, mewithoutYou have been slowly developing their unique style and gradually building up their touring credits by supporting such acts as Sparta and, most recently, Brand New and Thrice. But while they continue to grow in popularity, they remain dedicated to their hippie ethic, even going so far as to convert their tour bus to use waste vegetable oil instead of diesel fuel.

"Actually little-known fact about that is that we actually didn't 'convert' the engine", explains guitarist Mike Weiss. "There's not really much of a conversion, it's just that we put into place a system where we could filter and use waste vegetable oil, and make it clean enough for the engine to burn efficiently. All diesel engines will run on vegetable oil without any conversion. That was the idea, that farmers could cultivate their own fuel for the engine.

"We don't want to take precious petroleum that seems to cause a lot of political problems and wars and violence around the world and god knows what else, so the less of that that we have to partake in, the better. And it saves us money, that's another reason."

But it does come with its down sides. A replacement van had to be hired at short notice and excessive cost when they ran out of oil on the way to Seattle for a recent show, and maintaining a bus that runs on biofuel isn't exactly a picnic.

"It's a lot of work, it's very involved, you have to really be ready to get dirty and it's definitely not fun, but it's very important, it's very worth it for us."

Despite their best green intentions, in February next year the brothers Weiss will board a jumbo jet to fly down to Australia for their appearance at Soundwave festival, an exercise which will probably create more pollution than their clean bus has saved in its lifetime.

"I think that, ultimately, if we knew a way to get to Australia in time in a more efficient way, we would do it. [But] we just try to do what we can, you know, and the vege oil thing was just something that seemed pretty much like a no-brainer, that we could definitely do that at the very least."

Mike's, and especially his brother Aaron's, anti-consumption beliefs are borne out of their Christian faith, but seem to be rooted in a more humanistic interpretation of the Bible's teachings.

"I think that like, ultimately if you ask any of the members of the band their religious faith, we would all say 'well, I'm a Christian', but what that means to each of us can vary. I think that if you ask Aaron, the most important thing about his faith would be [the question of] whether we should be living extravagant lives by comparison to third-world countries. We're called to love our neighbor, but we as Americans, we hoard and we pillage the resources and we just live this lifestyle of decadence compared to those that are actually starving cause they don't have enough food.

"So I think if you wrap your mind around that, not saying I can, and I don't think Aaron can either, but I think the difference is that he's actually making a strong effort to live his life according to that question: 'how can I be loving these people when I don't suffer myself and I waste?' So to him it seems like that's a big part of his faith, whereas I'm not quite as extreme. I definitely believe that he's right but we differ on what to do about it."

Moving away from the heavy subject of religion, Weiss says that Aussie fans can expect something a little different from their usual shows when they get here for Soundwave.

"[Aaron] is going to be playing an accordion and I'm gonna be playing an acoustic [guitar], we're going to play our set with mewithoutYou songs, but they're gonna be different arrangements. Slightly different arrangements, but it'll be [mewithoutYou] songs and it'll be us playing, so it'll be awesome.

"We've played a lot of shows on this tour, we've built up our chops a little bit being on the road for the past year, we've been exposed to a lot of amazing music and yeah, we'll see what we get."

mewithoutYou join dozens of bands on the bill for Soundwave festival. You can check out their music on MySpace at www.myspace.com/mewithoutyou.