The paper first introduces the basic steps in the design of fiber-optic loose tubes for ribbon optical cables and briefly describes their main technological points.Then it explains the key points in the design by quantitative analysis and explains the issues for attention in their production on the basis of the production practice and puts forward suggestions for the selection and use of the fiber jellies as the important parts of the tubes.Finally

it experimentally verifies the effects of the jelly on the tubes and of the twist pitches on the cable performances and gives the curve diagrams of tensile tests in different twist pitches.