There are a few things to keep in mind when selecting fabric for a kitchen valance. Many kinds of fabrics just don't lend themselves to being a kitchen valance, for a number of reasons.
A kitchen valance is exposed to all kinds of abuse from the sun, kitchen grease and dust that comes in the window. A good valance should be of a fabric that will wash easily without looking worn, that won't fade easily and that doesn't demand a lot of maintenance. The list of bad functional choices for kitchen curtains and valances is long. Brocades are often dry-clean-only fabrics, linens are washable but take a lot of ironing and silks are easily rotted by sunlight. Luckily, fabrics like cotton, chintz and cotton blends do wear well and wash up easily. They still fade with time, but they're inexpensive enough to be replaced easily.
Some fabrics are just odd choices. Terrycloth, suedecloth, vinyl, jersey knits and fleece are all great fabrics in their own right, but none of them will enhance the look of your kitchen window.
Taste in window treatments is very subjective, but certain patterns lend themselves to kitchen use while others do not. In fact, there are some that really only belong in the kitchen. Food prints, chef prints and coffee-related prints are great for kitchens. Grapevines, florals, country patterns, simple stripes, geometrics or calicoes, while workable in many parts of your home, are also quite suitable for the kitchen. Often you can find coordinating fabrics so that you can mix and match some of these patterns. You should probably stay away from juvenile patterns like cars, kittens, or alphabets. Generally avoid "shiny" or flocked fabrics because they're overly-formal as well as impractical. Sheers and laces are fine as long as they are easily washable.