Many different materials: gut, nylon, steel, chromesteel, copper, bronze.
Yes, many have 5 strings
4 Strings.
You can play the Double Bass either arco. (which is with a bow) or pizzicato (which is plucking the strings).
4 Strings on a Double Bass
The double bass is much like the string bass, but it is also known as an upright bass, and commonly used in symphonies. It can be played with fingers, (pizzicato) but is usually played with a bow, like a violin. It looks like a big violin, and is played with the bottom of it, (opposite of where you tune the strings) at your feet, and the top around where your head is, while you are sitting down.
They usually have some kind of rope core that has steel wound around that. Here's a site that tells you about how Corelli strings are made. http://www.savarez.fr/anglais/corelli-double-bass.html
thicker strings
the double bass has 4 strings G string D string A string and E string.
its the same (but double bass strings are a whole lot more expensive).
Generally speaking, yes. The strings on a bass are longer than those on the nearest contender, the cello. They also tend to be thicker, because they are often made of different material. When cello and bass strings are made of the same materials, using the same processes, the G (top) string of the bass may be the same or smaller thickness as the C (lowest) string of the 'cello. But then, the bass continues down four more strings!
low to high - E A D G
new improved strings