About Plastic Welding Rods
Plastic welding rods are the consumable filler material used to join two plastic parts during hot-air welding. The single most important rule: the rod must be made of the same plastic as the parts you’re joining. Welding PVC with a polypropylene rod, or HDPE with a PEMD rod, will produce a weak weld that fails under stress.
The Plastic Welding Tools NZ range covers every common thermoplastic — manufactured by Techspan from virgin (un-recycled) material to ensure consistent flow and bond strength:
PP (polypropylene) — for polypropylene tanks, automotive battery boxes, ducting, and chemical fabrications.
PE-HD (high density polyethylene) — for HDPE pipe, large water tanks, geomembrane and landfill liner work.
PE-MD (medium density polyethylene) — for vehicle bumpers (most modern bumpers are PEMD), splash shields, and softer polyethylene products.
PVC — for rigid PVC plumbing, signage substrate, and cafe blinds.
ABS — for ABS panels, automotive trim, and 3D-printed-part repairs.
PP/EPDM — for thermoplastic-rubber blends used in vehicle interior plastics.
Rods come in standard 3 mm, 4 mm and 5 mm round profiles for most welding, plus triangular and rectangular profiles for fillet and butt-weld applications respectively. Common pack sizes are 50 m rolls for repair work and 400 m bulk rolls for production fabrication.
Not sure what plastic you’re welding? Our plastics identification guide walks you through the burn test, float test, and recycling-code lookups that will tell you whether you’ve got PP, HDPE, PEMD, PVC or ABS in hand.
Welding rod selection by plastic type
The single most important rule in plastic welding: the rod must be the same plastic as the parts you're joining. Welding PVC with a polypropylene rod produces a weak bond that will fail under load. Use the table below to pick the right rod for what you're welding.
| Rod material | Welds | Typical applications | Recycling code |
|---|
| PP (polypropylene) | PP parts | Tanks, automotive battery boxes, ducting, chemical fabrications | 5 |
| PE-HD (high-density polyethylene) | HDPE parts | Water tanks, HDPE pipe, geomembrane, landfill liner | 2 |
| PE-MD (medium-density polyethylene) | PEMD parts | Vehicle bumpers, splash guards, softer poly products | 4 |
| PE-100 | PE 100 pipe and fittings | Pressure pipe and gas distribution fittings | 2 |
| PVC | Rigid PVC | Plumbing, signage substrate, cafe blinds, flooring seams | 3 |
| ABS | ABS parts | ABS panels, automotive trim, 3D-printed part repair | 7 |
| PP/EPDM | PP-rubber blends | Vehicle interior plastics, soft-touch automotive trim | — |
Rod profiles and what they're for
Round rod (3mm, 4mm, 5mm)
The default for V-groove, butt and overlap welds. 4mm is the most common general-purpose size. Use 3mm for tight detail, 5mm for heavier sections.
Triangular rod
Purpose-shaped for fillet welds — the third face of the triangle fills the corner of a perpendicular joint, giving full coverage in a single pass.
Rectangular / flat rod
For butt-welding sheets and seams where a flat profile lays flush with the parent surface — common in membrane and tarp fabrication.
Pack sizes
- 25m and 50m rolls — repair work, occasional fabrication, when you only need a few metres of a specific colour.
- 400m bulk rolls — production fabrication where rod consumption is daily. Lower per-metre cost.
- 300m specialist rolls — some PEMD profiles are stocked in 300m for fabricators between repair-grade and production volumes.
Identification tip
When in doubt about a plastic part, look for a moulded recycling code inside (often under a flap or on the back). Code 2 is HDPE, code 4 is LDPE/PEMD, code 5 is polypropylene, code 3 is PVC. Our full identification guide covers burn and float tests for unmarked parts.
Frequently asked questions
What happens if I use the wrong welding rod?
The rod will either not fuse to the parent material at all, or it will form a weak mechanical bond that fails under stress. Different thermoplastics have different melt temperatures and are chemically incompatible — a PP rod will not bond to a PVC part, and a PEMD rod will not bond to an HDPE part. Always match rod to substrate. See how to identify the plastic you're welding.
How do I tell the difference between PE-MD and PE-HD?
PEMD (medium-density polyethylene) is softer and more flexible — used in most modern car bumpers, splash guards and softer plastic products. PEHD (high-density polyethylene) is rigid and harder — used in water tanks, HDPE pipe, geomembrane and chemical containers. The recycling code on most parts is the best signal: PE-HD is code 2, PE-LD/MD is code 4. See our plastics identification guide for the burn and float tests.
What size welding rod should I use — 3mm, 4mm or 5mm?
Match rod diameter to the joint thickness. Thin parts and tight detail work suit 3mm round. General-purpose welding uses 4mm round (the most common size). Heavier sections, fillet welds and long structural seams suit 5mm. Triangular and rectangular profiles are for specific joint geometries (fillet and butt-weld respectively).
Do welding rods expire?
Plastic welding rods do not expire as such, but absorbed moisture and UV exposure can degrade the rod over months or years. Keep rods in a dry, cool, dark storage. Rods that have visibly chalked, yellowed, or feel brittle should not be used for structural welds.
Can I use a triangular rod where a round rod is specified?
Not really — the rod profile is matched to the speed nozzle. A round-rod nozzle will not feed a triangular rod cleanly. Round rod is the universal default for V-groove and butt welds. Triangular rod is purpose-made for fillet welds where the third side fills the corner.
What rod is used for car bumper repair?
Almost all modern automotive bumpers are PEMD (medium-density polyethylene). Use a 3mm or 4mm PEMD round rod. Common colours are natural, black, and primer-grey to match. Check the recycling stamp inside the bumper before welding to confirm the plastic type. See our bumper repair walkthrough.
Need help choosing the right plastic welding rod?
Tell us about the job: the plastic you're working with, the wall thickness, and how often you'll use the tool. We'll recommend the right kit, welder or accessory for the application.
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