The softest organic towels I’ve found are Temesecal Towels from Coyuchi.
Temescal means “sweathouse” in Central America, and these towels are very light, fluffy and quick drying. They are made with long-staple Turkish cotton which is naturally soft.
The cotton is woven with narrow vertical channels for added drying power.
Temesecal Towels are GOTS certified, so they do not contain any bleaches, dyes other other chemicals.