Elastane blends present a massive hurdle for fashion sustainability, making garments nearly impossible to recycle or compost, with 60% of garments containing synthetic fibres and only 1% of them recycled yearly. Nursing bras are particularly challenging, requiring high elasticity and support while having short lifecycles as postpartum bodies change. The Gaia nursing bra solves this by offering an industrially compostable undergarment free from elastane and non-biodegradable plastics. The design combines 100% cotton knit fabric with 3D-printed flexible bioplastics, utilizing accessible, scalable fabrication tools like FDM 3D printing, laser cutting, and heat bonding to match the performance of traditional synthetic elastics. The backbone of the design lies in its metamaterial engineering. The straps and under-bust bands feature flexible bioplastics printed in parametric auxetic structures, providing inherent mechanical elasticity, encapsulated between layers of cotton fabric via heat bonding. Additionally, flexible heat-bonded stabilizers reinforce the laser-cut edges for a seam-free finish, while the adjustable clasps and nursing clips are fabricated from industrially compostable bioplastics. The Gaia delivers adjustable support while fostering a grounding connection between mother and child. By optimizing emerging biomaterials for high-performance apparel, the project provides a scalable blueprint to eliminate non-biodegradable elastic synthetics from the future of fashion.