Nowadays,　the　development　of　all-biomass　aerogel　fibers　that　integrate　robust　mechanical　properties　with　superior　thermal　insulation　remains　a　significant　challenge.　In　this　study,　all-biomass　core-shell　structural　aerogel　fiber　with　the　cellulose　acetate　shell　and　the　silk　fibroin　core　was　developed　to　address　these　issues.　The　resulting　cellulose　acetate-silk　fibroin　aerogel　fiber　demonstrated　impressive　mechanical　properties,　with　the　stress　and　strain　at　break　of　28.18　MPa　and　104%,　respectively.　These　properties　are　attributed　to　lithium　chloride-induced　slow　molding　and　heat　treatment-derived　crystallization　enhancement.　Furthermore,　the　cellulose　acetate-silk　fibroin　aerogel　fiber　possessed　excellent　water　resistance　and　easy　dyeability.　Notably,　based　on　the　multilevel　porous　structure,　low　thermal　conductivity,　and　core-shell　structure　of　aerogel　fiber,　the　knitted　fabric　exhibited　outstanding　thermal　insulation　performance,　such　as　a　|ΔT|　of　60.6　at　hot　stage　temperature　of　120　°C,　outperforming　previous　studies.　Consistent　with　the　experimental　findings,　the　numerical　simulation　results　revealed　that　the　exceptional　performance　could　be　attributed　to　the　macro-/nano-sized　pores　in　the　cellulose　acetate　shell　capturing　stationary　air　for　suppressing　thermal　conduction/convection,　and　walls　in　the　silk　fibroin　core　enhancing　infrared　reflectance　for　preventing　thermal　radiation.　This　innovative　approach　paves　the　way　for　designing　sustainable　aerogel　fiber　and　multifunctional　textiles,　with　promising　applications　in　personal　thermal　management.　©　2025　The　Author(s).　Energy　&　Environmental　Materials　published　by　John　Wiley　&　Sons　Australia,　Ltd　on　behalf　of　Zhengzhou　University.