These two ropes look similar hanging on a rack and they do almost nothing alike.
A speed rope is thin and light, often a coated steel cable, and the whole point is how fast it turns. You use it to build timing, foot speed and double unders. A weighted rope is thick and heavy, turns slowly, and loads your shoulders, arms, grip and core on every rotation. One trains your feet. The other trains your upper body while your feet keep time.
Where the weight sits, and why it decides everything
Some ropes put the weight in the handles. That gives you something to hold onto but the cord still whips around light and fast, so your arms work only at the start of each turn.
On the MONFIT Heavy Jump Rope the weight is in the cord itself, not the handles. The load is spread along the whole arc, so resistance is there through the entire rotation instead of at one point in it. That is the difference you feel in your shoulders after 90 seconds.
Pick by what you are trying to fix
Buy a speed rope when you want unbroken double unders, faster feet for a sport, or long low-effort rounds. Buy a weighted rope when your rounds already feel easy, when you want upper body conditioning without picking up a dumbbell, or when you have a small space and one tool has to do several jobs.
Plenty of people end up owning both. They are not competing for the same slot in a session.
What a weighted rope does to your technique
It slows you down, and that is useful. A heavy cord will not let you hide a sloppy turn behind speed. Your elbows have to stay in, your wrists have to drive, and your jump has to be low and consistent or the rope catches your feet and tells you.
Expect your unbroken numbers to drop hard the first week. Thirty seconds of a 3 lb rope is not thirty seconds of a speed rope.
Thickness and length, in plain terms
The MONFIT rope comes 1 inch thick at 3 lb and 3.5 lb, and 1.5 inch thick at 4.5 lb and 4.8 lb, in 9.2 ft and 9.9 ft lengths.
Start at 1 inch. It is heavy enough to feel completely different from a speed rope and light enough that you can hold a clean rhythm while you learn the timing. Move to 1.5 inch once you can run three unbroken minutes on the lighter cord without your form falling apart.
On length, the usual check works. Stand on the middle of the cord and pull the handles up along your body. The handle tops should land somewhere between your armpit and your shoulder. Shorter than that and you will clip your feet; much longer and the rope goes slack at the bottom of the arc.
MONFIT Heavy Jump Rope. Poly Dacron cord in a reinforced protective sleeve, textured heat shrink handles, carry bag included.
A first week that will not wreck you
Three sessions, 30 seconds on and 60 off, eight rounds. Single bounces only, no double unders, no crossovers. Your forearms will complain before your lungs do, which is the whole reason you bought a heavy rope.
Add time before you add weight.