The short answer
Supplying your own resin gives you control of cost and consistency, but only if you and the molder agree the details in writing first: the exact grade and color, who orders and when, buffer stock, drying, regrind, scrap allowance, storage, lot tracing and who owns leftovers. Ship to the molder's dock labeled with your PO and the lot number, and send the COA to both of you.
Many molders buy resin and build it into the part price. Others run customer-supplied (sometimes called consigned) resin, where the part owner buys the material and the molder converts it. Both models work. The second one needs more agreements up front.
Why companies supply their own resin
- Cost control. You see the resin cost separately from the molding cost, and you can buy in larger lots than a single job would justify.
- Consistency. The same grade and source go into every run, even if the part moves between molders or presses.
- The molder doesn't stock it. Specialty, colored or flame-rated grades are often not in a molder's inventory, and small volumes may not be worth their effort to source.
- Approvals. If a customer approved a specific grade, owning the purchase keeps it from drifting.
If you are buying resin for the first time, read how to buy plastic resin first.
What to agree with your molder
| Question to ask your molder | Why it matters |
|---|---|
| Which exact grade and color will you run? | Prevents substitution. A different grade, even in the same family, can change dimensions, appearance and approvals. |
| Who places orders, and how much notice do you need? | Avoids a press waiting on resin. Lead time plus transit sets your reorder point. |
| How much buffer stock should sit on your floor? | A safety stock covers late trucks and extra runs without tying up too much cash. |
| Who dries the resin, and to what moisture limit? | Wet resin causes splay or, in nylon, PC and polyesters, hidden brittleness. |
| What is your regrind policy for this part? | Regrind changes properties and may be limited by the drawing, a flame rating or a food-contact requirement. |
| What scrap allowance or yield will you quote against? | Sets how much resin you must supply per run and how shortfalls are settled. |
| Where and how will my resin be stored and labeled? | Keeps your material separate, dry and traceable to its lot. |
| How will you record which lot went into which parts? | Lets you trace a field problem back to a lot and its COA. |
| Who owns leftovers and regrind if the job ends or moves? | Avoids disputes over partial gaylords, regrind and material at the end of a program. |
| Is customer-supplied material covered by your insurance? | Your inventory sits in someone else's building; know who carries the risk. |
A starting checklist; your quality agreement or purchase terms may need more. Get the answers in writing.
Drying
Agree who dries, in what equipment, and to what moisture limit, and whether drying is in the molding price. Hygroscopic resins such as nylon, PC, PET and PBT must be dried before molding. See the resin drying guide.
Regrind and scrap allowance
Decide whether regrind is allowed, at what fixed ratio, and whether it must be the same grade and color. Flame-rated, food-contact and many automotive parts limit it. See how much regrind to use. Then agree a scrap allowance: the resin the molder may use beyond part and runner weight for startup, purging and rejects. Settle what happens if actual usage runs over.
Buffer stock and ordering
Set a reorder point from your usage and the supplier's lead time, and agree who watches the inventory. As a rule of thumb, keep at least one full package on the molder's floor beyond the current run. Ordering in gaylords rather than truckloads keeps less cash tied up; see small-quantity resin.
Shipping straight to the molder's dock
- Give the supplier the molder's full address, receiving hours and whether there is a dock.
- Put your PO number, part number if useful, and the molder's contact on the order.
- Ask that each gaylord or pallet be labeled with the grade, color and lot number, so the molder can receive it against your PO and keep it separate from their own stock.
- Tell the molder what is coming and when, with the expected weight and number of packages.
ResinBridge can ship straight to your molder: put the molder's city in the ship-to field and their name in the part or product field. Standard terms are FOB the warehouse.
Paperwork
Send the COA to both the molder and your own quality file. The molder checks the lot number against the label at receiving and records which lot went into which production run. Keep compliance letters (FDA, UL, RoHS) on file with your part records. See what a COA shows.
Common mistakes
- Ordering "the same material" by family name instead of the exact grade and color.
- No agreed scrap allowance, then a dispute when the resin runs out before the parts are done.
- Resin arriving outside receiving hours or without a PO, and sitting on a truck or getting refused.
- Your resin mixed into the molder's own stock of a similar grade.
- Undried resin, or a dryer sized for a different job.
- No plan for leftover material and regrind when the program ends.
What to send us for a quote
- The exact grade and color, or the data sheet
- Quantity per order and yearly usage
- The molder's city and whether they have a dock
We aim to send your quote within one to three business days.
Common questions
Why would I buy resin myself instead of letting my molder buy it?
To control cost and consistency. You see the actual resin price, you keep the same grade and source across production runs and molders, and you can supply a grade your molder does not normally stock.
What should I agree with my molder before supplying resin?
The exact grade and color, who orders and when, how much buffer stock to keep, who dries the resin, the regrind policy, the scrap allowance, how the resin is stored and traced by lot, and who owns any leftover material.
Can resin be shipped straight to my molder?
Yes. Most suppliers will ship to the molder's dock. Give the supplier the molder's address, receiving hours and dock details, and ask for your PO number and the lot number on the paperwork.
Who should get the COA when resin ships to a molder?
Both of you. The molder needs it to receive and check the lot, and you need it for your own records and traceability.
What is a scrap allowance?
The share of resin the molder may consume beyond the theoretical part and runner weight, to cover startup, purging and rejected parts. Agree on it in writing, so a shortfall at the end of a run is not a surprise.
Who owns leftover resin at the molder?
Whoever paid for it, unless you agree otherwise. Put it in writing, including what happens to partial gaylords and regrind if the program ends or moves.
Tell us the grade your molder runs
A polymer chemist reviews every request, then matches your grade or finds a qualified equivalent and prices it.
What to send for an accurate quote
- The grade name, from any supplier, or a data sheet
- Color (natural, black or a custom match)
- Fill type and percentage, if any
- Melt flow, if you know it
- Quantity for this order and what you use in a year
- Ship-to city and state or province