There are a couple of twine thicknesses available in the 4" mesh size nylon netting that Gourock supplies for volleyball barrier netting uses, and they are the #15 (1.7mm) and the heavier #30 (2.3mm). Both are fantastic for volleyball containment netting uses, and have their own set of preferred features. For instance, the #15 is most popular for indoor installations because there is no detrimental effect from UV exposure, and the thinner twine thickness minimizes the amount of material pre square foot (which means that the most amount of light can shine though, and the netting is minimally visible). The #30 is more popular for longterm outdoor installations, or for areas that expect higher amounts of wear/abrasion - such as commercial or high-traffic areas.
That said - both the #15 and the #30 can and are installed in both outdoor and indoor installations, and you can view/price/order them from this page of the Gourock site:
Many schools, training facilities, and commercial sports businesses require volleyball barrier netting to surround their individual courts from each other, as well as to block balls from passing into spectator areas. Here are a couple of example photos from Indoor Sand in Northwood, OH - a Gourock customer that installed the #15 X 4" knotted nylon netting for their volleyball containment purposes. You can check out their establishment at www.indoorsand.com - and thanks again, we appreciate your business!