What is the SK4390/BK4390 Touch Bar made of, and how strong is it?

The bar is made of extruded aluminum. 

It will not bend when used for its intended purpose of unlatching a storm or screen door. 

When installed correctly with the inside latch and support bracket, and with the storm door able to open freely, this bar will withstand normal usage for many years without any warping or degradation.

Please check out the instructions here for additional installation assistance.