All of my plumbing runs through copper lines in an accessible attic in a 1960's slab-on-grade ranch style home in Phoenix, AZ where I don't need to tell you how hot the attic can get for a huge chunk of the year. This results in having to run the cold water for about 2–3 minutes to get water that isn't scalding hot—and this "cool-down" of the pipes only lasts for maybe an hour before you have to restart the process as the pipes have heated back up again in the attic.
I know insulating the pipes will not entirely solve the problem as I will just be slowing down the heat transfer, but I'm trying to get some sage advice on whether it will be at least marginally effective (enough to justify the work) to insulate my water pipes. They sell polyethylene (pool noodle) pipe insulators here in the big box stores, but I also noticed a fancier version online which has a fiberglass interior with a foil-like radiant heat barrier and wondered if this would be better? Any advice or experience would be greatly appreciated. I've done a lot of searching online but can't find anything to answer my specific question.
update (12Sept2018) Thanks for all your answers and help everyone—I finished this project and wrapped the entire cold water line in the attic with the "pool noodle" type insulation. It made a noticeable difference in my house immediately. During the eight hours I am at work and no water is running through the pipes to cool them down the water still gets scaldingly hot, but once you run cooler water through the pipes it takes much longer to heat back up again to scalding (now it takes around 4–5 hours to heat back up rather than an hour like before). I have a temperature probe in the attic and during June/July it gets above 130F in the attic so there's a lot of heat to fight against.