The raw material we use is #1 Smoked Rubber sheet, which stretches like a surgical glove and can be compressed under load without splitting.  This is super important for avoiding pinch flats.
Many tubes are made of Butyl (synthetic) rubber which is artificial and lacks the natural characteristics, the stretching and compressing capabilities of natural rubber, meaning that when butyl tube punctures, it tend to split and tear (and almost impossible to patch/repair – not what you want when you’re miles from home). 
Natural rubber tubes repair and patch easily, and are a must for long distance riding. They aren’t cheap, but they aren’t expensive for what you get.

Standard Tube Motoz 100/100-18 110/100-18 3.25 x 18 3.50 x 18 3.75 x 18 inch