I first bought a Klean Kanteen in 2005. It was all it was cracked up to be. Sturdy, but light, water did not pick up a metal taste, it was easy to clean, and never leaked.
In early 2010, I decided to spring for a second bottle -- smaller this time, and with a nice painted color finish (not available when I got my first KK in 2005). Immediately upon receiving it, I could tell something was different. It felt thinner -- cheaper. Sure enough, I could squeeze the neck of the bottle and "squish" in the sides. I tried this with my original bottle. No way! It wasn't budging. I added water and, wow! The water had a terrible metallic taste. I never had this with the original bottle. I washed them both and filled them both from the same water source at the same time. Yup -- metallic taste from the 2010 bottle. No taste from the 2005 bottle. I started to wonder if the materials were the same, so I grabbed a small but powerful refrigerator magnet and tried to stick it to the side of each bottle. Remember, Klean Kanteen claims that the bottles are made of "304 stainless steel which has a low nickel content." (To be exact, 304 Stainless has between 8% and 11% nickel.)
Anyway, anyone with any knowledge of metallurgy knows that a magnet should not stick to 304 stainless steel. And, as expected the magnet does not stick at all to the circa 2005 bottle. But the 2010 bottle, even with the paint on it? The magnetic latched right on, even with the the bottle was turned upside down!
So, this and the metallic taste and the cheap construction leads me to believe that Klean Kanteen is NOT using the materials (304 stainless steel) they claim to use in these bottles. This is a serious accusation and not one I take lightly. But it is a serious concern. KK stakes their claim on providing high quality stainless steel. If they are using another material, they are deceivcing the public by not disclosing this fact.