A dense fabric without loops is prefered, that way nails do not get caught in the blankets. You could try double knitting. Also, man- made medium to dark color yarns that are hard wearing is recommended by the site (H4H Animals) and some shelters. If you have a particular shelter in mind it might be best to call them to see what they would like and or need. Blocked for design ideas don't forget to turn to a trusty stitch dictionary. HTH.