Composite Materials Shelf-Life & Storage – Part 3 – Expanding Foams, Cores & Vacuum Films

To finish up our series on composite materials shelf-life and storage we examine the consumables, including foams, cores & films.

Expanding Foams

Shelf Life of polyurethane expandable foams is generally ~6 months. After this period, the foams’ properties begin to degrade. Expandable foams should always be stored in their original containment and sealed appropriately, much like that of any resin storage. Expandable foams are not as susceptible to temperature variation as resins but are to moisture contamination and best stored sealed in a dry environment.

Core Storage

Composite core products, such as Nomex or metallic honeycomb or foam, do not have as tight restriction on shelf life in composites. However, its storage requirements are to be met with more delicacy. Many core materials are susceptible to handling damage. For core pieces it is important to store in original containment until the time for indented use. It is a good practice to sandwich core between flat sheets of cardboard for transporting core. This provides a degree of more rigid protection when handling core pieces. After opening, it is best practice to store all core pieces in a sealed bag with an added moisture desiccant bag to prevent moisture intrusion (silica gel). Once sealed, Nomex honeycomb, balsa, and foam are best stored at room temps in lower humidity environments (below 65%). It is also important not to touch core materials with bare hands as oils from our hands may transfer to the core materials causing possible delamination.

Vacuum Film Storage

Vacuum films do not have a defined expiration. Sealed vacuum bag material stored in a dry, dark indoor area at room temperature can last nearly forever when stored properly. However, like fabrics, vacuum films should be handled and stored with extreme caution and out of the high traffic areas of fabrication. Films are highly susceptible to punctures or misuse due to handling. Bagging film may easily be characterized by being fragile but not like glass breaking in an antique shop. For example, a heavier roll of exposed bagging film falling on any sharp object could ruin much of the film’s roll. Handling or storage damage is not something a fabricator will want to find upon bagging a part.