Why is the composition of the materials different between the colors?

Cotton fiber is dyed, not polyester.

Hence the mottled effect which is in fact a difference in reaction to the dyeing between the cotton and polyester threads.

That's why you need polyester to make heather.

Heather is always mixed with synthetic, otherwise it would give a solid gray result.

Cotton fiber is dyed, not polyester.

Hence the mottled effect which is in fact a difference in reaction to the dyeing between the cotton and polyester threads.

That's why you need polyester to make heather.

Heather is always mixed with synthetic, otherwise it would give a solid gray result.