Both these materials are weather-resistant and can be left outside year-round (though you will preserve the life of your hammock by taking it in during the off-season). They can be left out in the rain and will dry just fine in warm weather after the sun's been shining for a few hours. Both are color-fast and resist fading in the sun. Sunbrella is a softer fiber than olefin. It stands up particularly well in the sun. If you want a fabric hammock and you live in an area closer to the equator, like Florida or the Southwest, you're better off with Sunbrella. Olefin fabric is slightly less soft than Sunbrella, but is also less expensive.