Catgut suture treatment produces roughly twice the stitch-holding time of plain catgut, but greater tissue inflammation occurs. Full tensile strength is extended to 18–21 days. It is brown rather than straw-colored, and has improved smoothness due to the dry presentation of the thread (plain catgut is wet). It is otherwise similar to plain catgut. Fast catgut suture is heat-treated to give even more rapid absorption in the body. The first known absorbable sutures were made of the intestines of sheep. The manufacturing process was similar to that of natural musical strings for violins and guitar, and also of natural strings for tennis
Catgut as withstanding high tension within low alto, tenor, and high-bass ranges. Many acoustic guitarists moved away from gut strings in the early 1900s when the C. F. Martin & Company introduced steel strings, which gave greater volume to the guitar. "The demand for steel came from ensemble players, who couldn't make themselves heard clearly without it." Within a few years the majority of Martin guitars were made with steel strings to accommodate the demand. After World War II, most classical and flamenco guitarists switched from catgut to the new nylon strings for their greater smoothness, durability, and stability of intonation.