One of the most frequent request we get is to provide a Technical Data Sheet (TDS) for a given material. But do you know what you are getting, and how to use it?

First – a list of what a TDS is NOT:

  • “absolute values” – they are averaged values from many data points
  • “minimum values” – – same comment
  • “QA values” – these are not “go / no go” values

Technical Data Sheets are a comparative tool that allows you to see the general differences between materials in an organized format and is best used to compare materials from the same source!  Many mills use the resin data for their TDS, as it is the “lowest common denominator” – and there is a relatively limited pool of resin suppliers.

All thermoset suppliers (phenolics) and some thermoplastics mills test the actual shapes, but these are averaged. Think about it-cast nylon can be made in .187” or 10” plate – so exactly what is its tensile strength?

Some mills report ranges, technically more correct but makes comparing materials difficult – if one lists tensile is 13,000 – 15,000 psi and the other 14,000 psi, which is better?

Also – there is no direct correlation between ASTM and ISO/DIN values – the test samples and methods are completely different. Within each system, comparisons are usually valid.  Information on electrical properties, flammability, etc are always consistent and useful “as is”.

Not knowing the data source can have consequences. An airplane manufacturer specification required its supplier to use PAI rod with a minimum tensile strength of 22,000 psi. Their usual sources told them “in rod, it’s 18,000 psi”. Another source supplied a resin data sheet, listing tensile of 22,500 psi and won the order, but the parts ultimately failed. (NOTE: the key error here was with the airplane company, specifying extruded rod using resin data)

Examples of “data reporting  & terminology license” to watch out for:

  • Heat Deflection Temperature – the ASTM specification says you can run this at 66 psi or 264 psi.
  • Moisture Absorption – Most mills report 24 hr moisture pick-up, and full saturation values – but some report “equilibrium”, a number always lower than saturation to make the material look more stable than it really is.

Concerned or confused? Don’t be – the material experts at WS HAMPSHIRE can help you get the right information for your application evaluation. You’re in the right place!


Tom Connelly is a self proclaimed “Street Engineer” with over 40 years in the plastics industry.

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