How to choose EPS bead size: 201, 301, 302, 303, 401 and 501
Match the bead size to your product, wall thickness and target density.
Most Chinese EPS plants sort expandable polystyrene beads by size and give each fraction a code. The code tells you the range of raw bead diameters in the bag. Choosing the right one makes a real difference to how your moulds fill, how the surface looks and how low a density you can reach.
Bead size codes at a glance
| Code | Raw bead size | Typical products |
|---|---|---|
| 201 | 1.40–2.00 mm | Large blocks and insulation boards |
| 301 | 1.00–1.60 mm | Block moulding: insulation and building boards cut from blocks |
| 302 | 0.85–1.25 mm | Block moulding: insulation and building boards cut from blocks |
| 303 | 0.70–1.00 mm | Shape moulding: packaging, fish and fruit boxes, ICF blocks, foundation pods |
| 401 | 0.50–0.80 mm | Shape moulding: packaging, fish and fruit boxes, ICF blocks, foundation pods |
| 501 | 0.40–0.60 mm | Cups and food containers |
Start with your machine
The simplest rule is the type of machine you run.
- Block moulding machines make large blocks that are cut into boards. These plants usually run 301 or 302.
- Shape moulding machines make finished parts in a mould: packaging, fish and fruit boxes, ICF blocks and foundation pods. These plants usually run 303 or 401.
- Cup machines run the finest beads, 501.
Then fine-tune the choice
- How thin is your thinnest wall? The expanded beads must fit into the narrowest part of the mould with several beads across the wall. Thin walls, ribs and small details push you towards the finer end, 401 rather than 303, or 501 for cups. Blocks have no such limit.
- What density do you need? Larger beads reach low densities more easily. For low-density blocks and insulation boards, coarser sizes such as 201, 301 and 302 are the usual choice. Fine beads are normally run at higher densities.
- How important is the surface? Finer beads give a smoother, tighter surface. That matters for cups, visible packaging and decorative products, and much less for blocks that will be cut.
Size is only part of the choice
Bead size works together with the grade. The same size code can come as general purpose, flame retardant, graphite or cup grade material, and in different expansion series. Two shape moulding plants may both use 303, one making fish boxes from general purpose EPS and the other making ICF blocks from flame retardant EPS.
If you are changing supplier, send us a photo of the bag label of the EPS you use now, showing the brand and grade. We will suggest the closest matching NKL grade and bead size.