Why a Medical Plastic Part Does Not Come From an Ordinary Molder

A standard injection molding shop is a good place. It also has forklifts, cardboard, hydraulic oil mist, mold release spray, regrind bins, and operators handling parts with bare hands. None of that matters for a consumer housing. All of it matters for a part that will be sealed in a sterile barrier and inserted into a patient.

Terminal sterilization kills organisms; it does not remove particulate, it does not remove endotoxin from dead bacteria, and it does not remove hydrocarbon residue. Whatever is on the part when it goes into the pouch is on the part in the operating room. Cleanroom molding exists to control what lands on the part between the mold face and the sealed bag, and to produce the records that prove it.

What a Cleanroom Actually Is, and Which Class You Need

Cleanroom classes under ISO 14644-1 count particles per cubic meter. In practice medical molding lives in two places:

  • ISO Class 8 (roughly Federal Standard Class 100,000). The standard choice for most device components: housings, connectors, non-implantable fluid path parts, and anything that will be terminally sterilized in its final packaging. Air changes on the order of 20 to 60 per hour, gowning with smocks, hairnets, and gloves.
  • ISO Class 7 (Class 10,000). Used for implantables, IV and blood-contact fluid paths, ophthalmic products, and parts assembled aseptically. Roughly 60 to 100 air changes per hour, full gowning, tighter monitoring, and a meaningfully higher operating cost.

Class 5 molding exists but is rare and expensive; if someone tells you an ordinary housing needs it, ask why. Many programs also use a controlled environment that is monitored but not formally classified, which is legitimate for lower-risk parts as long as your quality system justifies it. Getting the class right is a risk decision, and it should come out of your ISO 14971 risk analysis, not out of a vendor's brochure.

What Changes Versus Standard Molding

The molding physics do not change. Everything around them does.

Machine configuration. Presses are typically mounted through the cleanroom wall, with the clamp and part-drop side inside the classified space and the hydraulics, motors, and oil outside. All-electric machines are common because they eliminate hydraulic oil near the part entirely.

Part handling. Parts drop onto stainless conveyors or are removed by robot directly into medical-grade bags, then heat-sealed inside the room. Nobody touches the part. Sprue picking, degating, and any secondary operation happen inside the classified space or the part loses its status.

No regrind, no shortcuts. Virgin resin only, single lot traceable to certificate of analysis. Mold release is generally prohibited outright, which means your part geometry has to eject cleanly on its own. That raises the stakes on draft, and the rules in draft angles and parting lines stop being guidelines and become hard constraints.

Tooling. Molds are built with cleanroom-compatible greases, stainless or coated steel to avoid rust and flake, and vents sized to prevent burning that would leave carbon residue. Tools are cleaned and requalified after any maintenance. That pushes most programs toward hardened steel rather than aluminum, a tradeoff worked through in aluminum vs steel injection molds.

Process discipline. Scientific molding with a locked process window, documented as IQ, OQ, and PQ. The OQ establishes the edges of the acceptable window; the PQ demonstrates capability, usually a Cpk of 1.33 or better on critical dimensions across three consecutive validated runs. You cannot adjust the process afterward without a change control record.

Medical-Grade Resins Are a Different Purchase

A medical grade is not just a cleaner version of the commodity grade. It comes with a certificate of analysis per lot, a master file or biocompatibility data package, a change notification commitment from the supplier so the formulation cannot shift silently, and often a regulatory support letter. Common choices include medical polycarbonate, polypropylene copolymers, COC and COP for optical clarity and low extractables, PEEK and PPSU for reusable instruments, and TPE grades for grips and seals.

Sterilization compatibility narrows the list fast. Gamma yellows many polycarbonates and embrittles unstabilized polypropylene, so gamma-stabilized grades exist specifically for this. Ethylene oxide is gentler on materials but requires residual testing and gas-permeable packaging. Steam eliminates most commodity thermoplastics. Choose the resin and the sterilization method together, not in sequence, using the comparison in medical device sterilization methods and confirming the result against ISO 10993 biocompatibility testing on the finished, sterilized part rather than the raw pellet.

The Documentation Is Half the Product

What you are really buying from a cleanroom molder is a records package: environmental monitoring data (particle counts, viable air and surface sampling, pressure differentials, gowning logs), full material traceability by lot, validation protocols and reports, first article inspection, and change control. The molder must operate under ISO 13485 and be prepared for your audit and potentially an FDA inspection, because as the device owner you are responsible for your supplier's compliance.

Ask concrete questions during selection: which ISO class rooms do you operate and what is your monitoring frequency; can I see a redacted validation package from a comparable part; who performs your particle counts and how often are they calibrated; what is your change notification process if a resin supplier reformulates; do you do bioburden testing in house or send it out.

What It Costs and When You Genuinely Need It

Expect a 20 to 50 percent premium on piece price versus the same part from a standard shop, and a larger premium on the one-time engineering because validation is real work. Tooling itself is often 10 to 30 percent higher for the steel and finish requirements. Lead times run longer too, since validation adds four to eight weeks after tool qualification on top of normal injection mold lead time.

Not every part needs it. A handheld monitor's outer housing that never contacts a patient can often be molded conventionally and cleaned before assembly. Split your bill of materials into patient-contact and fluid-path parts versus everything else, and put only the first group in the cleanroom. That single decision often saves more than any other cost reduction on the plastic side, and it should be made before you design tooling, not after you receive quotes.

Get the Parts and the Paperwork Right

Projects House designs medical plastic parts for cleanroom production, selects and qualifies molders, and runs the validation package through to approved first articles. Send your part drawings, contact classification, and target volumes through our contact form and we will tell you which parts genuinely need a classified environment.