The first step toward determining the amount of cushioning a product requires is to determine the amount of mechanical shock the product can survive on its own. There are several common terms for this, with "fragility" and "g-factor" being the most common.
Fragility is normally expressed in units of "g’s" and indicates the maximum deceleration the product can withstand without being damaged. The more fragile a product is, the lower its g-factor. The table below helps to illustrate this concept.
| Class | Typical Contents | Fragility |
|---|---|---|
| Extremely Fragile | Missile guidance systems, precision aligned test instruments | 15-25 g’s |
| Very Delicate | Mechanically shock-mounted instruments and electronic equipment (Shock mounts should be firmly secure prior to packaging. They are provided for in-service protection only.) | 25-40 g’s |
| Delicate | Aircraft accessories, electric typewriters, cash registers and other electronically operated office equipment | 40-60 g’s |
| Moderately Delicate | Television receivers, aircraft accessories | 60-85 g’s |
| Moderately Rugged | Laundry equipment, refirgerators, appliances | 85-115 g’s |
| Rugged | Machinery | 115 g’s and up |
Ideally, the fragility of a product is determined by subjecting it to a series of gradually more severe shocks (decelerations) in order to find the lowest severity impact that will damage the product. The highest deceleration, which did not cause damage, is then known to be the product’s g-factor.
It may be necessary to determine fragility levels for a product in various orientations, as it is not uncommon for a product to exhibit greater strength in one direction than another. Even very similar models should be tested individually as it’s seldom that fragility for one model may be safely assumed from another.
There is no substitute for fragility test data. Educated guesses as to a product’s fragility are often counterproductive to the design process. If the g-factor is estimated too high, and the product is unable to survive as much shock as anticipated, the packaging will be underdesigned and significant shipping damage is likely to occur. On the other hand, if the g-factor is estimated too low, and the product can actually withstand more shock than anticipated, the packaging will be overdesigned and unnecessarily expensive.