We propose an approach to enhance the reversibility of thermochromism in polydiacetylene-based nanostructures, which are known for switching between blue and red colors in response to temperature variations. It was achieved by derivatizing 10,12-pentacosadiynoic acid (PCDA) and embedding the formed self-assembled nanoplatelets in an alginate matrix prior to photopolymerization that leads to a thermochromic 2D conjugated system. Amide groups were introduced to PCDA by reacting with (N-aminoethyl)acetamide to strengthen the network of hydrogen bonds between the molecules that enabled the formation of stable bilayer nanosheets as imaged by AFM and verified by molecular modeling. The use of alginate as a polymer matrix significantly improved the stability and reversibility of the thermochromism of dispersed PCDA-based nanosheets likely due to the formation of hydrogen bonds between them and alginate chains. The best reversibility of the thermochromic behavior was obtained in 0.001% alginate aqueous medium as followed with bare eyes and quantified using colorimetric response calculated as the level of recovery of the blue band (‘‘percent blue’’, PB = 44%). Gelation of the system with Ca2+ ions increased the reversibility to PB = 68% due to immobilization and separation of the nanoplatelets in the polymer matrix that was further improved after drying to reach PB = 70%. The resulting nanocomposites combine high stability with the ability to respond to thermal stimuli in a controlled manner, making it an attractive system for applications in colorimetric sensors and smart polymer materials including fibers where reversible thermochromic properties are highly desired.