I'm about to install drip edge on a roof before putting down a torch down roofing material. I have found two types of 2x2 drip edge. One has two little bumps in the top surface. You can see what I mean in the second outline down on this page:
Styles of drip edge, choose the proper edging for your roof installation. (http://www.rainguttershop.com/edging.htm)

The other type is completely smooth across the top (no bumps). Is one better than the other? I have bought the smooth type but am anxious to install because I heard a "rumor" that the bumps make water running back under the lip of the torch down less likely. Is this at all true? Why are the bumps there in the first place? My first impression was that smooth might be better because it would lead to better stick from the torch down.

Thanks in advance for any insight!

I use the bumps for 3 reasons.

1. Doesn't kink easily.

2. The extra bump helps keep water out.

3. My guys have a guide to nail it in the middle and keep the kinks out. Number 3 was a job joke.

It's a matter of what manufacture one gets used to. The drip edge is to drip Not stop eve freeze or water blowing back. The roofing is supposed to do that.

The only purpose "bumps" or "crimps" serve on drip edge, fascia or other aluminum coil stock products (othern than for decoration) is to stabilize the metal and make it less prone to bending when shipping and handling.

The bumps and crimps also permit the use of smaller gauge metal to be used, and therefore make the products less expensive.

It does not matter, therefore, which type you use.