Commitment to Quality

This article has been created to help our customers try and disseminate between the various levels of (poor) quality of carbon fibre sheet and moulded composite products in the market now. Whether you are building a UAV, robotics, End-Of-Arm-Tooling, making clay modelling splines/slicks, dashboards, instrument panels or any project utilising carbon fibre this is a quick guide to what you should avoid.

First thing you need to know – Not all carbon fibre sheet is created equal!

“But isn’t carbon fibre the ultra-high performance black stuff that the likes of NASA, USAF and F1 use?” I hear you say. Well yes you are right; carbon fibre is truly a wonder material of the modern age possessing high strength and stiffness. To be more precise pure carbon fibre has a specific strength  around 11 times  greater  than  aluminium  &  10  times greater than steel in addition to a specific stiffness more than 5 times greater than aluminium & steel whilst being around 5 times lighter than steel, 2 times lighter than aluminium.

What affects the quality of carbon fibre sheet and moulded composite products?

A number of things but to be brief there are 3 main aspects that affect the quality of the final carbon fibre sheet and moulded composite product, including:

  1. Selection of high quality carbon fibre and using only carbon fibre (filling up the thickness of the carbon fibre sheet with cheap grade carbon or even worse fibreglass is BAD!) – This is important because of Rule of Thumb no.1.
  2. The manufacturing process should be a closed mouldprocess that applies pressure to the stack of carbon fibre plies that make up your sheet (the carbon fibre is only strong and stiff because of the carbon fibre NOT the resin/plastic that holds it together. In addition the carbon fibre sheet must not have pinholes/voids, which are far more than just cosmetic defects but in fact severely reduce the mechanical performance of the carbon fibre sheet  – This is important because of Rule of Thumb no.2.
  3. Minimising distortion of the carbon fibre fabric during layup and moulding, where large distortion is generally easy to spot on the surface of the carbon fibre sheet as an odd looking ripple in the fabric. If your carbon fibre sheet has a large varation in thickness (>0.5mm) then this could also be a sign of excessive distortion of the carbon fibre. This is important because of Rule of Thumb no.3.

How to tell if it’s BAD quality?

To illustrate what is bad we have bought and tested 5 different carbon fibre sheets sourced from various suppliers of carbon fibre sheet. You will never see any of the following defects in carbon fibre sheets and moulded composite products manufactured by Juno Composites Ltd – Guaranteed!


Rule of Thumb no.1: For the best performance carbon fibre sheet the use of the highest quality carbon fibres (T700 or equivalent) and epoxy resin is essential. See what happens with carbon fibre sheets that often only contain one single layer of carbon fibre and the rest is fibreglass and resin.

Rule of Thumb no.2High percentage of carbon fibres in the sheet = High performance Carbon fibre sheet = GOOD! See a zoomed in picture of a not so good competitors carbon fibre sheet that is peppered with pinholes/voids (circled in red) on the surface of the carbon fibre sheet. Remember that for each and every 1% of voids/pinholes in the carbon sheet leads to a 10% reduction in performance (and it looks awful too!).

The next picture taken with a microscope is a section cut through the thickness of the same competitors 2mm thick carbon fibre sheet. It shows that the pinholes on the surface are in fact inside the carbon fibre sheet too and that the carbon fibre content is very low which is bad because of Rule of Thumb no.1.

Rule of Thumb no.3: The carbon fibre sheet is only strong and stiff in the direction that the fibre flows in. Large deviations in the principal fibre directions from distortion of the carbon fibres looks awful and is bad for performance too!

Large distortions in the carbon fabric can also be indicated by a sudden variation in thickness of the  carbon fibre sheet – or it just could be that the manufacturer has missed out a layer of carbon fibre!

Are these defects normal?

No! You should not have been supplied a carbon fibre sheet that possesses any of these defects unless the manufacturer makes clear that they have lifted it out of their scrap bin! Unfortunately these defects are present to some degree in 4 out of the 5 carbon fibre sheets that were sourced and tested. Chiefly we think it arises from a lack of expertise and knowledge both in the design of the carbon fibre sheet and the selection and execution of the manufacturing process to produce carbon fibre sheets of high quality at a competitive price.


 About Juno Composites Ltd:

Juno Composites are fast becoming the largest supplier with the widest range of engineering carbon fibre sheets in the UK and Ireland and the ONLY manufacturer to guarantee performance having tested all our structural carbon fibre sheets in conformance with British (BS ISO EN) and American (ASTM) standards so that when you choose us you know you’re getting the best performance and quality.  If you would like to see any of the technical data sheets for our carbon fibre sheets please visit

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