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Magnetorheological Fluid

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Magnetorheological fluid, or MR fluid, is a type of fluid that becomes more viscous when exposed to a magnetic field.[1] Using an electromagnet to vary the strength of the field, the physical resistance of the fluid can be varied. Commercial MR fluid can be approximated with a mixture of micron-sized iron powder in oil.



Lord Corporation has a detailed recipe for MR fluid. I've repeated it here with additional notes.


  • Latex gloves, because it can get messy.
  • Paper towels to clean up that mess.
  • Something for measuring out volume or weight. A scale is ideal, but measuring spoons will suffice.
  • A chopstick or any other non-metallic object for stirring and evenly measuring iron powder.
  • A container for the MR fluid, at least 100 ml.


  • Multi-purpose oil like 3-in-1 Oil. It shouldn't be an aerosol like WD-40, but in a "drip can".
  • White lithium grease like Lubrimatic's. Again, non-aerosol: it will come in a cardboard can or a tube.
  • 1-10 micron iron powder. Powders are sometimes rated using meshes, for example <200 mesh meaning 74 microns or less, see this conversion chart. Fine iron powder is sold by Science Lab, Micron Metals, and on eBay. A list of suppliers is available from ThomasNet.

The oil and grease can be found at home improvement or automotive stores. I found mine in the hardware section at Home Depot for about $3 each.


Proportions are originally given by weight. I've added some approximations for volume, drawing the specific gravities from the 3-in-1 oil datasheet and the a white lithium grease datasheet.

  • Oil 55g / 60.7 ml (from experimentation, this might be a little high)
  • Grease 5g / 5.26 ml
  • Iron 150g / 49.6 ml


  1. Pour oil and grease into container
  2. Close and shake container for 5 minutes
  3. Allow mixture to sit for a few hours
  4. Mix in iron
  5. Shake container for a few more minutes


Lord Corporation also sells MR fluid at exorbitant prices.[2]

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This page was last modified on 6 July 2007, at 06:45.
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