Tunnel stabilization matrix
This resource is accessible right from the beginning of the game and extremely common. If you collect even a tiny portion of it in the tunnels it will never be depleted.
It is used to slow down or stop inside a warp tunnel. You will need 5 units of it for each second you are completely stopped inside the tunnel, or proportionally less if you just want to slow down.
Sometimes it can be hard to know if you are speeding or breaking so you can watch the speedometer at the bottom of the screen. If the pin is in the middle, you are running at normal speed. In this picture we are going a bit faster than normal.
If the speedometer is pointing to the left, you are moving slower than normal and using stability matrix units. If it is all the way to the left, you are stopped and using 5 units every second. In this picture, we are almost stopped.
You can accelerate for free at any time. In this picture we are going twice as fast then the normal speed. Accelerating brings you no advantage other than helping you to time your landings when you jump or covering larger gaps in the tunnel with a single jump.
You can see how much you have left on the lower right side of the screen. That bar represents 500 units, that is 100 seconds of full stop. If you have more, the bar will be full. You can have a maximum of 50,000 units of this resource in your inventory.
Slowing down and stopping (youtube video).