Modifiers matching shell:

• protective,
• polymeric,
• outer,
• hard,
• large,
• individual,
• attractive,
• fossil,
• regular,
• globular,
• soft,
• diverse,
• hollow,
• cortical,
• insoluble,
• delicate,
• external,
• thermoplastic,
• waterproof,

Simple categories matching thermoplastic:

• film,
• polymer,
• synthetic,
• material,
• compound,
• fibre,
• substance,
• tube,
• component,
• powder,
• substrate,
• fiber,
• elastomer,
• part,
• article,
• coating,
• polyester,
• matter,
• particle,
• sheet,
• container,
• system,
• shell,
• filament,
• foam,
• shape,
• fabric,
• adhesive,
• process,
• waste,