these are usually made from 2mm diameter rope which is often reflective and can be adjusted using a small plastic locking device
cheap versions just use a flat plastic locking device with two holes but these are prone to slipping
a better design is the micro-locking plastic devices designed for 2mm cordage which will not slip and these are available in noctilucent material which is more visible at night
can be used with hiking tarps as well as hiking tents
2mm Dyneema inner/polyester outer reflective cords are probably the best you can get as they are light and offer 200kg breaking strain which should cover the needs for ANY tent
cheaper 2mm standard reflective polyester cordage usually has a breaking strain of 100kg
cheaper 3mm standard reflective polyester cordage usually has a breaking strain of 135kg but will not fit the 2mm micro-locking devices