This review is just shy of 2 years since the purchase of my first Bose SIE2i Sport Headphones. Since that time, I have made my way through the original purchased pair as well as a replacement pair. I'll start by saying these are some of the most comfortable and best sounding sports headphones I've tried. After working my way through 5 to 10 different headphones for running and cycling, I spent the extra money and purchased these at the recommendation of a colleague. Once I tried them on, I didn't believe they would stay in my ear as they were so comfortable but I never once had an issue with their fit. They were excellent headphones for about six months...Now, to why I gave these headphones two stars (it would have been one if not for the comfort and fit). My first pair of Bose SIE2i Sport Headphones began having issues with the volume controls and microphone within six months of purchase. This didn't concern me as I typically don't alter the volume much during a run or ride and certainly don't take calls. I have other Bose noise canceling headphones for my non-exercise needs so I decided I could live with the problem. However, as I wore the headphones the volume began to go all the way up or down, randomly. This can be quite a problem when on a bike ride and the volume maxes out. Soon after this began, I took the headphones to a Bose store and they replaced them with very few questions asked (great customer service).My second pair of Bose SIE2i Sport Headphones fit and worked as good as the previous version for, again, about six months when the volume controller and microphone began acting up again. Given I was past my year warranty on the original pair at this point, I decided to ride it out. With the second pair, I didn't have the random volume swings as before but the sound quality would fade in and out. This was all manageable up until about a week ago when the left earpiece completely lost functionality. Well, today both earpieces completely failed during a run. The earpieces themselves didn't appear to have much in the way of wear and tear so I took apart the volume control/mic, which is where the problem seemed to start. FYI, you basically have to destroy the headphones to do this but I figured I didn't have anything to lose at this point. The small board inside had lots of corrosion (see photo) on or near the button controls and where the wires entered the control housing.From what I can tell, it appears sweat got in the mic opening as there was only mesh and some foam there, which doesn’t appear to be water proof. There was also some infiltration at the wires enter the housing. Given that water and sodium (sweat) are quite corrosive (think about ocean air), it appears the electronics failed after exposure.Now I used to tolerate problems from the $20 headphones I previously purchased but expected a lot more from Bose given these advertise "Sweat- and weather-resistance, using hydrophobic acoustic cloth". Oh, and the price. I expected a lot more from $100+ headphones.At this point, I am going to look into options other than Bose for my exercise headphone needs (twice is enough). While I'm a dedicated Bose fan (I own two pair of noise canceling headphones and a bluetooth speaker), I'll likely try the Jaybird X2s as they have a similar looking fit mechanism and a lifetime sweat guarantee - wireless is nice too.