Once you find the size that fits (I started with a large and worked my way up), these work very well.  They are a heavier fabric than other 'regular workout' leggings I have, so will keep you a bit warmer.  I used them in 75 degree days and 75 degree water.....got a bit chilly in the water after 30 minutes....and never got too warm out of the water. The string at the waist if a bit useless to me, but if you have a very narrow waist, it might help keep them up.