Ropes are getting thinner and thinner. However, this doesn't seem to directly translate to reduced weight as the difference between different ropes of same diameter is surprisingly large.
Sub 8mm half ropes are not rare anymore with at least Tendon Master 7.8TendonMaster 7.8http://ecx.images-amazon.com/images/I/51oZmMseLBL.jpgAn excellent rope with uncompromising quality certified both as a half and twin rope. Low weight and top-class specifications enable broad versatility but it‘s ideally suited to ice and mixed climbing. (7.8mm, 38g/m), Mammut TwilightMammutTwilighthttp://static2.mammut.ch/medias/sys_master/8815869755422/7.5_Twilight_grass_bild2.eps_Zoom2.jpgThe latest version of the well-known Mammut® double rope has resulted in the thinnest half rope in the world: The 7.5 Twilight now meets the standards for half and twin ropes, making it the perfect companion for two-person rope teams on long demanding tours on rock, ice and in mixed terrain. The COATINGfinish™ treatment guarantees long-lasting protection from dirt and water during these alpine pursuits, ensuring consistently high performance. (7.5mm, 38g/m), Edelrid ApusEdelridApushttp://www.vaude.com/out/pictures/generated/product/1/1024_1319_75/71042_138.jpgUltra-light twin and double rope. The ideal solution for mixed routes, alpine sport climbing and extreme mountaineering, where every gram counts. (7.8mm, 42g/m), Sterling Rope Fusion PhotonSterling RopeFusion Photonhttp://www.sterlingrope.com/dimg/f7e4e565c8b22e6abc510d29e747baf0.jpgThe Fusion Photon is Sterling’s first half rope that is also certified to twin. It was manufactured to have a perfect balance of diameter to weight. Designed to round out the Fusion series as a performance half rope, the Photon is small and light, making rope drag less of a concern over long or windy pitches. (7.8mm, 42g/m), Petzl PasoPetzlPasohttp://www.petzl.com/files/imagecache/product_outdoor_slideshow_zoom/node_media/paso-0_1.jpgWith a diameter of 7.7 mm and an extremely light weight, the PASO 7.7 rope is designed for ice climbing or technical mountaineering in cold, wet conditions. This rope benefits from the Duratec Dry treatment to improve longevity and performance in any conditions. (7.7mm, 42g/m) all being sub 8mm ropes. The thinnest and lightest of the bunch is Beal GullyBealGullyhttp://blog.weighmyrack.com/wp-content/uploads/2013/10/Beal-Gully-73mm-Unicore-GoldenDry.jpgWeighing only 36 g per metre, the GULLY 7.3 is the lightest double rope on the market. It is also certified as twin rope. Its extremely light weight and very low impact force make the GULLY 7.3 the ideal rope for ice climbing, mountaineering and the most demanding terrain. Like all other thin double ropes in BEAL's range, the GULLY 7.3 benefits from the reliability and additional safety that UNICORE technology provides. at 7,3mm and 36g/m. Obviously worth a look for all activities where grams per meter is top of the requirement list.
While looking at weight per meter, the difference between different ropes of same diameter is surprisingly large. For example Tendon and Edelrid offerings have the same diameter, yet Tendon is 4g/m lighter. Which equals roughly 10% percent. Quite a bit IMO, maybe even to the point of raising suspicion about the accuracy of the measurements.