Infeld Blue Series 4/4 Size Violin Strings 4/4 Size Set. Thomastik Infeld Red and Blue strings are relatively insensitive to humidity changes, break in quickly, and have a relatively low tension. A new synthetic, composite core gives Infeld Red and Blue strings a full sound and a longer life span than other synthetic strings. The Infeld strings are also responsive to different playing techniques. Red strings have a darker tonal quality and Blue has a brighter tonality. Each corresponding individual string, Red or Blue, has the same tension. This allows the player to achieve tonal preference in a single string brand without the headaches of uneven tension. Removeable ball on E string.