Nairobi's slums face significant environmental challenges due to rapid urbanization and inadequate infrastructure. Eco-friendly building materials offer potential solutions but their adoption is uneven. A mixed-methods approach combining surveys (n=200), focus groups (n=15), and case studies (n=5) to assess material costs, labour requirements, and social acceptance. Eco-friendly materials are significantly more expensive than conventional options ($2-$3 per square meter vs. $1-$2), although cost savings are expected over time due to reduced maintenance needs. Community engagement is crucial for successful implementation. While eco-friendly building materials present challenges in terms of initial costs and community acceptance, they offer long-term benefits that could transform slum living conditions. Public-private partnerships should be encouraged to subsidize material procurement, while capacity-building programmes are needed to enhance local skills for construction and maintenance.