Let me try and get this forum going in the right direction. Hopefully I will generate some constructive dialogue.
Here is what I have learned about raw denim through reading many articles from many diverse sites.
1. All cotton will shrink. Unsanforized more than sanforized. Washing in a machine shrinks more than soaking. Hot soaking will shrink more than cold water soaking and keep more indigo on your jeans.
I always soak my new denim sanforized or not. The temperature depends on how the jeans fit me. If they are loose I soak in hot water, if they fit correctly I use cold water. This approach helps keep the creases in the same place when I eventually wash them.
2. After I soak my new denim I let them drip dry in the sun, but I don't let them dry completely. When they get to a slightly damp stage I put them on. This lets them stretch out in the right places, and when they dry on your body the creases set in tight. I find this is a better alternative to siting in a tub with my jeans on. Wearing soaking wet jeans around the house is not very fun. One last thing, soaking new denim for more that 20 minutes is a waste of time, because the cotton gets saturated in 20 minutes. If you go longer than 20 minutes you're just losing indigo.
3. The heavier the denim, the less they stretch out over time.
4. This is a quick way to get your stacks to set. With your jeans on take a garden hose and spray the bottom of your denim. It does not have to be super soaked, just wet works fine. After you get them wet put on shoes that you don't mind getting indigo dye on. Next, just slightly push them down and wear them, gravity will do the rest.
5. I feel that the more your jeans flex and stretch the better your fades will progress. For this reason I would never use starch on my jeans. If you think about it, starch stiffens your denim and keeps it from flexing and moving. Some believe that starch is to abrasive and will shorten the life of your prized purchase.
Well, that's what I do.
Some info here is incorrect.
1 - Soaking itself does not shrink denim, nor does the temperature. Or atleast, well water temperature is a contributing factor, but agitating the denim is what causes denim fibers to fill themselves with water and tamper the weave and yarns. When the fibers dry, the weave tightens itself and thus denim shrinks. Temperature for drying has most influence on shrink, this is one of the reasons tumble drying jeans is not advised.
2- Indigo is not soluble in water. It does not matter if you soak for 20 minutes or 20 days. The only thing that will come of is starch and exces indigo, which you don't want anyway. I agree with the fact though, that soaking for periods longer than 20/30 minutes is useless, the cottonfibers are saturated with water after a while, like you allready mentioned.
3 - While heavy denim is harder to stretch due to the tickness of the fabric, doesn't mean they stretch less. There are more factors that play a role, like the tightness of the weave, what kind of cotton is used etc.
Just some insight, not trying to be wise here or get on your back.