# Pyro Shredding Question

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Hi,

From houdini docs : "Temperature threshold : At temperatures lower than this value the velocity field will be stretched, at temperatures higher than this the velocity will be squashed"

Question: is it supposed to be the opposite? meaning at lower temperatures squashes velocity (i.e. temperature is already low, so push vel down further), and at higher temperatures stretches velocity (to make higher flames/licks)? Plz see attached image

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I think I got it, with high temperature, vel is already high, so we need to squash it (otherwise will get super long smoke like shapes), and vice versa

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What version of Houdini are using? In newer versions of Houdini shredding is just disturbance (take a look inside the solver). Not sure if the gas shred dop is still there, but the docs you are quoting sound like they have been taken from that operator.

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If memory serves the old shredding method would allow you to pick a target temperature to act as a boundary. The temperature gradient would then be calculated which in essence make vectors that pointed in or out, away from the boundary. The vectors on the inside acted as the "stretch" and the vectors pointing out acted as the "squash" . I found the terms squash and stretch to be missleading. As you increase the size of the "stretch" the velocity vectors pointing in increase the pressure on the inside. The increased pressure causes the velocities in the bouancy direction to increase, hence the term stretch. The squash work in the opposite way. I found the easiest way to understand what this dip did was to copy the vex code inside it and put it in a wrangle sop. Sops is a much more intuitive place to figure out what's going on

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