Long story short, a group of 8th-graders are investigating the alleged suicide of one of their classmates after finding her dead body hanging from a tree in the woods. They try to follow one of the only clues they can think of, which is the type of rope used, and they go to a hardware store in town to ask what type of rope it is and if anyone had bought it recently. The store owner, who I imagine likes to nerd out about his job whenever he has an audience, tells them what type of rope it is and what the rope is used for. Then Mr. Red Herring comes in, Old Man Prescott, who buys a ton of that exact type of rope, which gets the kids suspicious (for entirely baseless reasons, as one of them will eventually point out), and they investigate him. Old Man Prescott is actually using the rope in his wildly-unsafe and-out-of-control pet project on his farmland, a massive abomination of a treehouse-slash-playground that he keeps obsessively adding onto in his free time, and his plans for the rope are for a sort of climbing area. With that in mind, I'm trying to work out what type of rope it would be that he was buying, and by extension, what the store owner would tell them about what it would be used for, and how common it would be for other people to buy it.
All the playgrounds around here use iron chains on everything except rope railings on platforms more than 2 feet off the ground. Those ropes appear to be nylon based.
Yes, I haven't seen much rope used on playgrounds, but it was always nylon because organic ropes like cotton or hemp would rot quickly from getting wet.
You can probably get away with something simple. Like a brightly colored orange rope with blue dots or something. I think you said it was set in Idaho from the other thread? If it's the 90s and it's a small town that only has one or two stores that sell rope, it shouldn't be too hard for the kids to investigate. Especially if it's a false clue used to keep the plot moving.
As a former tent-maker, I have bought and sold a lot of rope. My guess is that the playground stuff would have been polyester (of which Dacron is the most common trade name). Much more durable than nylon, holds up better to the elements. Other ropes might include polypropylene (weaker, but useful for applications that require the rope to float) or natural fibers like sisal and manila, which are the cheapest but not very durable.
To answer this question I think you need to answer a few others first. What is the rope being used for on the playground? Is there a theme to the playground that would require rope? A rope swing could use anything that met the strength requirements. But if the playground had a ship theme with rope bridges, then the designer might go with more natural fibers, than synthetics, just to fit the theme of the place.
I remember the rope they used at my school's playground in the early 90s. For climbing, tire swings, guardrails. There wasn't a ton of rope, but what was used was all organic. I don't know the material, but it was beige, and it was a bit bristly. If you slid down that rope, your hands were going to be pretty sore, and you might end up picking little rope hairs out of your skin. But like others have said, there's plenty of room for variety here, and there aren't going to be a lot of rope expert readers who are going to call you out on the choice you make. I did a quick image search for fun, and was a little shocked to see almost the exact same playground model that we had at school. It was mostly wood, so yeah, plenty of splinters. They must've sold these playground kits all over. Spoiler: big image
Beige and bristly is probably some sort of hemp rope. They wouldn’t have been too concerned with decay because playground ropes are replaced every 5 or so years anyway standard hardware store rope is generally blue and made from either nylon or polypropylene, it’s not used in playgrounds because it tends to degrade in sunlight and can very easily break when it’s a year or so old high tensile applications like a death slide are generally made of a steel core in a a nylon sheath
