EPS, expanded polystyrene, is a rigid foam made of small polystyrene beads fused together with pockets of trapped air between them. PUR, polyurethane, is a rigid foam formed by reacting two liquid chemicals together so they expand and cure in place, trapping gas inside a closed-cell structure as they set. Both insulate by trapping a gas and stopping it moving, not by blocking heat directly. The gas is the insulator; the foam is just the cage that holds it still.
The two rarely compete for the same job. EPS is molded into standalone panels and box liners before it ever meets the product. PUR is usually foamed in place, injected as a liquid into a cavity, a shipping box wall, or a cold store panel, where it expands and sets around whatever it is filling. That difference in how each one is made ends up deciding cost, thickness, and where each one gets specified. Packaging engineers choose between them at the design stage, long before a single shipment is booked, because the foam choice sets the box's wall thickness and cost for every shipment that follows.
Thermal performance per millimetre
PUR's closed-cell structure traps a lower-conductivity gas than the air pockets in EPS beads, so PUR insulates better at the same thickness and needs meaningfully less material to hit the same target hold time. EPS needs more thickness to match it, which matters on a shipper where every extra centimetre of wall eats into the payload volume inside a fixed outer box size. On a thick-walled cold store panel that difference matters less; on a small parcel shipper competing directly with product space, it can decide the box design outright. Neither foam changes that relationship once it is molded: performance per millimetre is fixed by the cell structure chosen at manufacture, not by anything done to the box afterward.
Cost and how each is shaped
EPS is one of the cheapest rigid foams to produce and mold: beads go into a reusable mold and get steam-fused into a fixed panel shape at scale, which keeps unit cost low for high-volume, standard-size shippers. PUR costs more per unit volume and needs its liquid components mixed and poured or injected on site or at the factory, which adds equipment and process control. In exchange it can be foamed directly into an irregular cavity or an existing outer box, filling a shape EPS could never be molded into without a custom tool. A packaging buyer ordering thousands of identical parcel shippers a month leans toward EPS for exactly this reason: the tooling cost is fixed and the per-unit price keeps falling with volume.
Moisture and durability
EPS is a poor place for water. Its bead structure absorbs moisture over time, and a wet panel loses much of its insulating value, so EPS shippers are usually kept dry by an outer carton and used once or a handful of times before the foam is retired. PUR's closed-cell structure resists water penetration far better, which is part of why it is the standard fill for permanent cold store wall and roof panels that face condensation and washdown for years rather than one trip. A food distributor running a reusable tote through a wash-down cycle every trip needs the water resistance PUR provides; an EPS liner would not survive more than a few cycles in that environment.
Panels, shippers and permanent structures
EPS dominates low-cost, high-volume passive shippers, parcel-scale packaging, and disposable box liners across food and pharma distribution, anywhere the box is used once and price per unit matters most. PUR shows up in reusable insulated containers built for many cycles, and it is the standard core material in the wall and door panels of built cold rooms and cold stores, where its moisture resistance and thinner wall for the same performance pay for the higher material cost over a building's working life. Vacuum insulated panels sit above both on performance per millimetre, at a cost premium neither foam carries.
Picking the foam for the job
Neither is the better insulation outright. A high-volume, price-sensitive, single-use shipper is usually built around EPS: cheap, easy to mold at scale, thick enough to do the job on a lane where box size is not the constraint. A reusable container, an irregular cavity, or a permanent structure exposed to moisture over years calls for PUR instead, where the thinner wall and better water resistance earn back the higher material cost. Decide by cycle count and moisture exposure first, thickness budget second, and let cost follow from those, not the other way round. Neither foam is being phased out. Each keeps winning the jobs suited to how it is made.