The difference comes down to fiber vs. weave:

100% Cotton

• What it means: The fabric is made entirely from cotton fibers.
• Feel: Depends on how it’s woven or knit — can be crisp, soft, thick, thin,etc.
• Breathability: Usually very breathable and good for sensitive skin.
• Note: “100% cotton” doesn’t tell you the texture or finish — just thematerial.

 Cotton Sateen

• What it means: It’s still cotton but woven using a sateen weave (a specific
  pattern of threads).
• Feel: Smooth, silky, slightly shiny surface.
• Look: More luxurious, with a subtle sheen.
• Warmth: Slightly warmer and less breathable than plain cotton weaves
  because the threads are packed closer together.
• Common uses: Bedsheets, pillowcases, and higher-end fabrics.

Simple way to remember:

• 100% cotton = what it’s made of
• Cotton sateen = how it’s woven