PACKING MATERIALS AND THEIR APPLICATION Foam Cushioning Materials Foam products are used to absorb the shock and vibration for art objects inside packing boxes or crates. It is commonly known that the largest shocks to a crate occur during the handling in transit. When the crate is being transported, the possibility of it being dropped or knocked over is hard to predict, but we can determine the severity of the shock based on the size and weight of the crate. For example, an oversized painting crate is more likely to experience a lower drop height than a smaller crate that can experience a higher drop height. The packing industry and the military have done extensive research in the various modes of transportation. Based on this information we can predict a probable drop height of any size of crate based on the maximum drop it might experience. Foam packing materials provide shock protection by allowing the packed object to sink into the foam on impact thereby reducing the maximum rate of change of velocity (or the peak acceleration) experienced by the packed item. The foam dissipates the energy of the drop and to minimize the effect to the object. It is crucial to choose the proper type of foam as well as the correct amount of foam. Too much foam would prevent the object to compress into it and the shock would go directly to the object. On the other hand, too little foam could cause the object to compress too much into the foam and possibly bottom out to the crate bottom. Manufacturers of the various foams have provided dynamic cushioning curves that help us predict which foam to use and how much is needed for any given object.
Protection against vibration is provided by the internal damping of the foam material that can dissipate vibrational energy in varying degrees before it reaches the packed object. The main concern with packing against vibration is to avoid having a loose contact between the packing materials and the object. This could result in surface abrasion of the object shifting during transit. Resilient foams, such as those made of polyethylene (etha foam), polyurethane-ester type (ester foam) as opposed to those made form polystyrene (styro foam) are best at providing protection against repeated impacts because after they are compressed, they have “memory� so that they recover most, if not all of their original thickness. If non-resilient foams like polystyrene are ued and repeated impacts are encountered, this foam had no memory and gets compressed. The object can become loose and shift inside the crate. If this occurs there may not be adequate protection available for subsequent impacts. The most common material used for crating and packing is polyethylene. Following are the basic foam products we use in packing cases and which can be used when softwrapping objects for transit: Cross-link Foam: This closed-cell polyethylene foam, which is off-white in color and is related to etha-foam and volora. It is commonly used for packing sensitive objects for long-term storage. Some conservators will require it used when bracing objects into an enclosed