...

When selecting a plain duvet insert, quality should be a top priority. Look for inserts made from high-quality materials such as goose down, synthetic fibers, or cotton blends. Goose down inserts provide exceptional warmth and lightweight comfort, while synthetic alternatives offer hypoallergenic options for those with sensitivities. Cotton-filled inserts, on the other hand, provide a more breathable and cooler sleeping experience, ideal for warmer climates.

...

However, there are lower quality cottons used in sheet making as well. Upland cotton is one of the most common. Because of its lower quality, it is often cheaper than Egyptian or Pima/Supima cotton. Additionally, organic cotton of any variety is generally more expensive than non-organic cottons.

...