Cobweb
The Cobweb is a special block that slows down entities moving through it.
Cobwebs are intangible in the sense that the player can move through: they do not have a collision box.
But cobwebs do have an "effect box" that is 0.001b smaller than a full block. If the player's bounding box intersects with this effect box, their velocity will be set to 0 and their movement will be hindered.
In particular, the player is able to stand next to a cobweb if they are at most 0.001m away from the edge.
In that case, the player is able to move normally while "touching" the cobweb's borders.
Effect on Movement
Vertical Movement:
Vertical speed is slowed down by a factor of 20, and is reset on every tick.
Jumping is severely limited, and reaches just 0.021m[1] in height.
The player will then immediately start falling at a constant speed of -0.00392 m/t[2].
Horizontal Movement:
Horizontal speed is slowed down by a factor of 4, and is reset on every tick.
This means the player will move at a constant speed of 0.03185 m/t when sprinting on ground, or 0.00637 m/t while airborne[3].
Or, respectively with 45° Strafe, 0.0325 m/t when sprinting on ground, and 0.0065 m/t while airborne[4].
Calculations: