I use braided cotton clothesline. It is a medium weight in size 7/32". I have used 3/16" size, which is usually sold at quilt/fabric stores, but I can not always find that size. I sometimes find a good braided cotton rope/clothesline at Ocean State Job Lot stores, and they sell it in different lengths. I usually purchase the large roll of 200 foot for $10. I also order online the same size thru Amazon, but the line is not as stiff. I have been to many hardware stores and Home Depot and they carry the cotton clothesline for $2-5 more.
Please send me where you find good clothesline and I will post it here, on my blog. Thanks.