Instruction: Extract information from the supporting document to answer the given question.

Input:
Question: Is the pole spring tensioned, or is it a locking slide tension?
Document: The rubber grips on the foot of the caddy keep it from coming loose or even wiggling. The combination of the sturdy pole and locking, slide-to-adjust shelf system means even my large, economy size bottles are supported without issue. I love that the shelves are easy to adjust even while in-shower, without the need to take down the entire apparatus.
I owned this shower caddy for 4 years - the packaging states "5 year warranty" and "rust proof" but unfortunately I did not keep the receipt (did not purchase from amazon.com). Sometime during the 4th year, all of the shelves developed rust on them. I don't shower with eyeglasses on and didn't even notice, but once the tension spring started to lose its strength this past year, the pole fell a number of times, spilling its contents all over the tub.
This is an engineered main pole that has heft and looks great. The parts all slide on with ease and position quickly and securely. I have held two other shower caddies and neither of them was worth a darn. This is worth the extra money. I will never buy a simple round rod caddy again.
I did see some earlier posts that said that when you slide the baskets on the pole that they were scratching the pole, but the shelf clips now have a rubber grommet underneath so this does not happen.There are 2 extra extension poles depending on how tall you need it, anywhere from 6 ft. to 9 ft.  No cutting pieces with a saw to make them work, like many of the other cheap caddy's.It has a 5yr.
I love this shower pole. It is easy to install if directions are carefully followed. It will fit an eight foot ceiling or higher, having alternative extensions. I love the look. It is clean looking and beautiful. I was able to position the shelves to be very accessible to me. As a short person, I always have had trouble with shelves that are too high. Also, the products placed on the shelves do not slide or fall through the shelves because they are solid.
Once it was assembled, it was great. The directions need to be clearer. I am quite good at figuring out how to assemble things, but I found this less than clear.I recommend that you don't try to slip the baskets directly onto the main pole as the directions indicate. Instead, slide them onto the top pole, THEN insert the top pole into the main pole and THEN slide the baskets down onto the main pole.
I have always liked simplehuman, and I figured this would be up to their high standards. Still, I am really impressed by the quality, simplicity, and utility of this item. You take it out of the box, slide the pieces together in five minutes or less, and put it up like a vertical tension rod.
There are plastic parts on this... so I can't comment on the long term durability of them yet. The internal spring in the pole is of course key to the gizmo continuing to stand... and so far..... it's still standing strong. Nice!
Even at $129 (which I paid for at BBB) I suppose nothing is rust "proof" unless you spend top dollar for a very high-end piece of equipment that would most likely not be a tension-spring design. I'd prefer to purchase replacement shelves, rather than spend $130 every 4 years.
I needed one of these but didn't want to spend this much on a shower caddy. That was a mistake. The $30 one I bought lasted a mere 6 months and it rusted out and fell down. Picked this one up as I originally should have when it was a Lightening Deal on Amazon.This is quality and good design. The tension spring is in the bottom piece and pushes up on the top piece into the ceiling.
Answer: It is a pole spring rension.  Still works perfectly.  Nice quality.