How do I choose the right compostable resin grade?
Match the grade to four things, in order: your processing method (thermoforming, injection moulding, blown or cast film, extrusion), the end application and its mechanical demands, the finished thickness or micron, and the certification you must hold. Get the process match right first: a film grade will not injection-mould well, and vice versa.
Only after those four are fixed should you fine-tune colour, additives, and dosage. A supplier who asks about your machine and application before quoting is giving you the right grade; one who offers a single all-purpose resin usually is not.
Start with your processing method
Compostable grades are formulated around a process window. Thermoforming grades are tuned for sheet extrusion and forming of trays and containers; moulding grades for injection of rigid parts like cutlery, caps and closures; film grades (blown or cast) for bags, wraps and mulch; and laminate or coating grades for barrier layers. Running a grade outside its window causes tearing, poor seals, or dimensional problems.
Tell your supplier the exact equipment and temperature/speed profile you run. Good compostable grades are designed to process on standard machinery with only minor adjustments, but the starting grade has to be the right family.
Match mechanical needs and thickness
Different applications demand different tensile strength, elongation, puncture resistance, and seal integrity. A 30-micron carry bag and a 100-micron mulch film are very different jobs even though both are film. Specify the micron range and the performance the part must survive in real use, not just the average, but the worst case.
This is also where you decide between grades within a family. Anjaneya's granules span a 30 to 110 micron working range and can be customised, so the grade is chosen to hit your spec rather than forcing your product to fit a stock resin.
Confirm certification and colour without breaking it
Whatever grade you choose, the finished product must still meet the compostability standard you claim (IS/ISO 17088, validated through CIPET-accredited testing and CPCB registration). This matters most when you add colour: ordinary masterbatch can introduce heavy metals or non-compostable carriers that quietly void certification.
Use a compostable colour or additive masterbatch designed to preserve the claim, and keep the test reports and certificates for your own EPR records. If a coloured or filled grade cannot show compostability data for the finished article, treat the claim as unproven.
Key takeaway
Choose a compostable resin grade by process first (thermoforming, moulding, film, laminate), then application and thickness, then certification and colour. The right grade processes on your existing equipment and keeps the finished product certified compostable under IS/ISO 17088.