Polyurethane Ester Foam
Polyurethane Ether Foam
Ester vs Ether
Ester and ether foams are very similar to each other in manufacture and appearance, and the lack of brand names at the consumer level combined with casual labeling can complicate the identification of polyurethane foam offered by some regional foam suppliers. The table below lists the relative qualities of each in in comparison to the other, and in the context of art handling.
| Ester Foam | Ether Foam |
| Slightly Smaller Cells | Slightly Larger Cells |
| More Supporting & Effective Cushion | Inadequately Supporting Cushion |
| Greater Strength | More Fragile |
| Relatively More Chemically Stable | Considerably Less Chemically Stable |
| More Expensive | Less Expensive |
| Considerably More Insulating | Considerably Less Insulating |
| Susceptible to Hydrolysis | Resistant to Hydrolysis |
| Less Common among Suppliers | More Common among Suppliers |
The only factors in ether's favor are the lower cost, wider availabilty, and resistance to breaking down when wet. Its softer compression characteristics are not necessarily a benefit in this case. 2 pcf ether tends to be soft to a fault for most objects, compressing too much and thus failing to provide sufficient cushioning support. This is not to say that ester is chemically stable, or that it is always the right choice for a cushioning material. But for use with art objects, preference between polyurethanes lies overwhelmingly in favor of ester foam.
Although two distinct grays are shown in the photo below, ether and ester can at times be found with nearly identical charcoal color. In such cases, it takes a trained eye to spot ether foam, and sometimes a pinch as well. Ester will tend to sparkle slightly and look more textured, while ether will tend to look smoother and more homogenous.
See this link for more information on the differences and backgrounds of ester and ether, provided on The Foam Factory website. More technical information is available online in the DOE report prepared by J.P. Madden, G.K. Baker, and C.H. Smith, "A Study of Polyether-Polyol- and Polyester-Polyol-Based Rigid Urethane Foam Systems."
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