Ultrablack wool textiles inspired by hierarchical avian structure.

Wildlife often uses a combination of colors in their skin, scales, and feathers to both attract mates and avoid predators. Some animals express an extreme level of black color, called "ultrablack" with reflectance <0.5%. The various nano/microstructures that produce ultrablack have been studied and replicated synthetically. These synthetic ultrablack materials, however, use highly advanced and costly techniques, toxic substances, and lack the flexibility and biocompatibility that are often desired in real-world textile applications. Here we show that a conventional natural fabric can be transformed into an ultrablack one with a biocompatible dye and a surface modification to create nanofibrils. The ultrablack wool fabrics we report have an average total reflectance of 0.13% (λ = 400-700 nm) and represent the darkest fabrics currently reported. Unlike commercially available ultrablack fabrics, the ultrablack wool developed in this study remains breathable and conformable. Furthermore, it exhibits wide-angle ultrablack performance, maintaining a symmetric (angle-independent) optical response across a 120° angular span. Environmental and mechanical tests also prove the material's resilience, showing the retention of its natural fabric characteristics alongside its ultrablack properties. To demonstrate the manufacturability in the textile industry, we present multiple parameter sets for plasma etching to achieve the ultrablack effect.