Why ultra-low RI matters
Anti-reflective performance is fundamentally determined by the refractive index contrast between stack layers. The larger the difference between the high-RI and low-RI layers, the fewer layers are needed to achieve a given reflection target — and the broader the spectral bandwidth of the AR effect.
With Kriya's LRI at 1.16 paired with HRI at 1.95, a two-layer stack achieves broadband reflection below 0.5%. Reaching RI 1.16 without fluorinated chemistry was the single hardest problem in Kriya's platform development. Its solution unlocked the entire PFAS-free AR capability.
Beyond AR stacks, ultra-low RI coatings serve as waveguide cladding layers. In diffractive waveguides for AR/VR headsets, the cladding must provide a large RI contrast with the waveguide core to maintain total internal reflection and efficient light guiding. RI 1.16 cladding paired with RI 1.85 core gives a delta-n of 0.69 — enabling compact, efficient optical designs.
The overcoatability challenge
Low-RI coatings typically rely on porosity — engineered voids that reduce the effective refractive index below that of the bulk material. Porous coatings inherently resist overcoating: the next layer's solvent or resin infiltrates the pores, collapsing the structure and raising the RI.
Fluorinated low-RI coatings avoid this problem by using dense fluoropolymers with inherently low RI. But they are PFAS. Removing fluorine and maintaining both low RI and overcoatability required Kriya to develop a novel pore-sealing approach that preserves the mesoporous structure while rendering the surface compatible with subsequent coating layers.
The result: Kriya's LRI at RI 1.16 can be overcoated with HRI, hardcoat, anti-smudge, or other functional layers without RI degradation. This enables stack architectures where the low-RI layer sits in the middle of the stack — not just as the topcoat — unlocking design freedom for multi-functional coating systems.
PFAS-free formulation
Kriya launched its 100% PFAS-free LRI in 2025, replacing all fluorinated components including surfactants, processing aids, and functional groups. The PFAS-free LRI achieves:
- Refractive index: 1.16 (measured at 589 nm)
- 100% PFAS-free throughout the formulation and manufacturing chain
- Full overcoatability with Kriya HRI and functional topcoats
- Adhesion: 100% on PET, PC, PMMA, and TAC substrates
Performance across substrates
The LRI coating has been validated as part of complete AR stacks on common display and optical substrates. When paired with Kriya HRI (product codes 006, 106), the resulting AR stacks deliver broadband reflection below 1.5% on polymer films and below 0.5% with additional layer optimisation.
Mechanical durability is maintained by the basecoat and hardcoat layers in the stack. The LRI layer itself is protected by its position within the multi-layer architecture and by the overcoat adhesion enabled by Kriya's pore-sealing technology.
Processing compatibility
Kriya's LRI is supplied as a solvent-based coating ready for:
- Spin coating — laboratory and pilot scale
- Dip coating — batch processing for complex shapes
- Gravure and slot-die — R2R production at industrial speed
- Spray coating — large-area substrates
Thermal cure at moderate temperatures (compatible with polymer substrate limits). No UV cure step required for the LRI layer, simplifying the coating line when used in multi-layer stacks with UV-curable HRI layers.
Paired with Kriya HRI for full AR stacks
The LRI coating is designed to work as a system with Kriya's HRI nanoparticle dispersions. This single-supplier approach eliminates cross-compatibility risk and simplifies qualification. The combined RI range of 1.16 to 2.00 is the widest from any PFAS-free supplier globally, enabling AR stacks previously achievable only with fluorinated materials.