EVA foam arrives here in rolls, around 1.2 m wide, in sheet thicknesses from 1 mm up to 10 mm, and it leaves as a molded shell, a die-cut insert or a laminated panel. Understanding the material is mostly about three numbers: density, hardness and how it behaves under heat.
What EVA Foam Is
EVA is ethylene-vinyl acetate, a closed-cell copolymer foam. The vinyl acetate content sets how rubbery it feels; higher VA gives more flexibility and better low-temperature performance. It is not the same as EPE (expanded polyethylene), which is lighter and cheaper but has a coarser cell structure and poorer shape recovery, and it is not PU foam, which is open-cell and absorbs water. EVA's closed cells are why it floats, why it does not wick, and why it can be heat-formed.
Density for case work runs 0.15-0.25 g/cm3, with 0.18-0.22 covering most of what we mold. Hardness is quoted on the Shore C scale, typically 40-70, and the two numbers move together but not proportionally - two sheets at the same density can differ in hardness depending on the blowing agent and the cross-linking. Cross-linked EVA recovers better after compression and takes a cleaner die-cut edge; non-cross-linked sheet is cheaper and adequate for flat liners.
How It Is Processed
Compression molding is the main route for hard cases: a cut blank goes into a heated aluminum cavity, the press closes, and the sheet takes a three-dimensional form with walls usually 1.5-2.5 mm. Cycle time runs 60-90 seconds depending on thickness and the cooling arrangement. Thermoforming, where sheet is heated and drawn over or into a mold by vacuum, suits shallow trays and large panels but gives less control over wall thickness at deep corners.
After forming, the shell is trimmed, then sewn or laminated. Common surfaces are 600D Oxford for abrasion resistance, velvet or flocked finishes for linings, and PU leather for a retail look. Inserts are die-cut from flat sheet or, for conforming shapes, built up in two or three laminated levels; egg-crate foam is used as lid padding where a screen or a polished surface needs give.
Where EVA Loses
EVA is not the answer to everything. Below about minus 20 degrees C it stiffens, and a case dropped on a frozen loading dock behaves differently from one dropped in a heated warehouse. It creeps under sustained load, so a case stored fully packed for months takes a small permanent set. It is not a fire-rated material unless compounded for it. And for very high-volume single-cavity consumer packaging, injection-molded PP or ABS beats it on unit cost, which is why the range also includes aluminum frame cases and molded ABS and PP boxes. Environmental and compliance questions come up on nearly every quote now. Compounds carry RoHS and REACH declarations with CTI reports on file, CA Prop 65 statements are available for the US, and recycled-content sheet can be specified at a cost premium that most buyers accept only above the 3,000-unit tier.
Anti-static grades for electronics are checked against IEC 61340-5-1. The next batch of sheet arriving this week is 0.22 g/cm3 at Shore C 60, and the first job on it is a run of insulated medical cases for a repeat customer.