Physics Van 3-site Navigational Menu

Physics Van Navigational Menu

Q & A: Sawdust and Styrofoam

Learn more physics!

Most recent answer: 10/22/2007
Q:
why is ’saw dust’ a better insulator than styrofoam
- skeete (age 16)
bishop anstey high school, trinidad and tobago
A:
Well, which material you choose as an insulator depends on what you want your insulator to do. Sawdust isn't a better insulator for many kinds of jobs.

Styrofoam is generally lighter than most sawdusts because it has a higher fraction of air in it. Air cannot flow through styrofoam as easily as through sawdust, and so sawdust may have a greater convection component to its thermal conductivity than styrofoam. Sawdust comes in many different kinds -- the particles may be fine or coarse, affecting its thermal insulation properties.

One advantage of styrofoam is that it can be made into rigid containers. While the strength isn't great, it is enough to make a coffee cup or a cooler out of. With sawdust, you'd need some kind of rigid container to hold it, or you'd have to glue it together, which would increase the thermal conductivity.

Styrofoam may be cheaper to buy, but there is a lot of sawdust made anyway and you might be able to get all you want for free from someone just waiting to get rid of it. Some kinds of styrofoam, when they degrade, release halons into the environment which have been implicated in ozone destruction high in the atmosphere, so sawdust may be more environmentally friendly.

Styrofoam melts at temperatures which are readily attainable in the kitchen. Don't put a styrofoam cup on a hotplate or in the oven -- it will melt. Sawdust, on the other hand, can catch fire.

Your question just said "insulator" and I answered so far only about thermal insulation. You can imagine other kinds of insulation -- electrical and acoustic, for example. Due to the possibility of connected paths for air to flow through sawdust, and the fact that air will allow electricity to flow through when the voltage is high enough (it will "break down" and allow a spark to go through), I'd imagine that sawdust is a poor choice for an electrical insulator. Also the catching-fire part doesn't help in this case either. Styrofoam isn't a good choice for electrical insulation either. As for acoustic insulation, the sawdust may actually work better because the dust particles are able to move and slide against each other, dissipating sound energy better than a piece of styrofoam, which may just reflect the sound or vibrate coherently.

Tom

(published on 10/22/2007)

Follow-up on this answer.