Cotton and Cotton Polyester (Cotton Poly Ropes) blended rope is a very weak rope, but it does have its common uses because of its low cost, low weight and flexibility. This video demonstrates the strengths and weakness of these ropes.
Cotton and Cotton Poly blended rope has a very poor strength. They have very short fibers so that means less fiber on fiber friction is produced so less overall strength. Also, these short fibers cause it to lack abrasion resistance and shock loading. They also lack stretch because of these short fibers. Because of the Cotton fibers, you can actually bend these ropes, so they are quite flexible. They can tolerate UV very well which is demonstrated with the old clothes lines that were so commonly used. They also are by far the best in price per square foot.
In survival, you can burn the cotton ropes easily, so you could use them to start a fire. If you have a Cotton/Poly blend you would have to separate the Poly sheath because that would just melt when put to a flame. They are very light to carry, but due to its poor strength it has limited uses in a survival situation. It is also rarely used in rescue due to its poor strength and flexibility. You would not want to use this in rappelling because of its poor strength. They are commonly seen in commercial use with tying bundles or lashing.