A cloth made of wool and linen mixed, and a traditional Jewish prohibition from wearing it. Leviticus 19.19 exhorts the Jews not wear a mingled stuff, wool and linen together…
Scholars such as Josephus suggest this was to prevent the laity from wearing priestly garb, others such as Maimonides put forward that heathen priests wore such mixed garments, tying it to the general principle of not mixing different kinds–in this case animal and vegetable fibres. It could also be for practical and health reasons; perhaps to do with the way the different cloths react on the body in hot climates.