A sensor may include a knitted pocket and loose yarn that is inside a cavity of the pocket. In some cases, this loose yarn is neither woven, nor knit, nor otherwise part of a fabric. A resistive pressure sensor may include a knitted pocket and loose conductive yarn that is inside the pocket. Pressure applied to the pocket may compress the loose yarn, which may increase the number of electrical shorts between different parts of the loose yarn, which in turn may decrease the electrical resistance of the loose yarn. A capacitive sensor may include a knitted pocket and insulative loose yarn that is inside the pocket. A strain sensor may include knitted conductive pleats. Electrical shorts may occur in contact areas where neighboring pleats meet. As the strain sensor stretches, these contact areas may become smaller, causing the electrical resistance of the pleats as a group to increase.