When choosing the right material for your valances & kitchen curtains, you'll probably take into account the décor style of the room. However, depending on their location and proximity to the sink or stovetops, don't forget about practical issues such as washability, fire resistance and need for privacy.
If you're mainly buying curtains to have a bit more privacy, prioritize heavier fabrics or those with blackout linings; on the contrary, if your focus is on decoration, choose lighter, airier materials for a billowy feel;
Linen and flax-based fabrics are ideal for longer curtains: while they can be more expensive, they're also incredibly durable and perfect for frequent washing;
Cotton is a lighter option, but still reliable and easy to wash; it can discolor after being exposed to direct sunlight for years, but, being cheaper than linen, these curtains can be easily replaced;
Synthetic fabrics come in lots of varieties, don't wrinkle nor fade from sunlight, and are usually the cheapest; however, they're also the most flammable, so we only recommend them for very high valances and curtains that are far from your stovetops;
On the contrary, some synthetic fabrics like Trevira and Avora were specifically made to be fire retardant, so they're actually the best options for valances & kitchen curtains that are a bit too close to your hobs.