Kilayim 9:1-2

Kilayim 9:1

The prohibition against shaatnez (a garment of mixed fabrics) only applies to a combination of wool and linen. Also, wool and linen are the only fabrics that can be rendered ritually impure through tzaraas (generally translated “leprosy” but actually a spiritual affliction). The uniforms of the kohanim in the Temple only included wool and linen. If camel’s wool and sheep’s wool were combined, then if the majority is camel’s wool, it may be combined with linen; if the majority is sheep’s wool, it may not be. If it contains equal parts camel’s wool and sheep’s wool, it may not be combined with linen. The same rules apply if linen is mixed with hemp.

Kilayim 9:2

Silk (which resembles flax) and tussah silk (which resembles wool) are not prohibited because of shaatnez but they are rabbinically prohibited because people will mistake them for flax and linen, respectively. There is no issue of shaatnez for mattresses and pillows so long as one’s skin does not come into contact with them. One may not wear shaatnez even passingly, nor even on top of ten other garments, not even to avoid paying customs taxes (i.e., if one has to pay for luggage but not for the clothes on his back).