Styrofoam is a lightweight plastic that is made of 95 per cent air, according to the Earth Resource Foundation. It is used for school projects, packaging materials and disposable food containers. Because this type of material is made of mostly air and plastic, it is full of holes and can melt, which makes it difficult to find an appropriate glue to adhere either styrofoam to another piece of styrofoam or to other items. Most glue types can be used, as long as the adhesive does not contain a solvent -- it can erode the styrofoam. There are certain glues, however, that provide a stronger hold than others.
The best glue to use is specifically-made styrofoam glue. Popular brands make styrofoam-specific adhesives, such as 3M styrofoam Spray Adhesive, Floracraft Styro Glue and Hold the Foam. Most of these styrofoam glues can also be used on other craft projects. Clear in colour, all of the styrofoam-specific glues permanently bond with little mess.
Silicone/Flexible Epoxy Glue
Silicone and certain epoxy adhesives have durability, temperature, water and air resilience and can be used on almost every surface. These types of glues are clear and flexible, so it can form around curves and fill in gaps, ideal for styrofoam, which is porous. It can also be painted, which is another benefit for styrofoam craft projects. Brands such as E6000, General Electric, LePage, Loctite and Permatex, along with others, make these adhesives. Each brand is different, but it usually dries fully in 24 hours.
Hot glue on plastic can be dangerous, as it can possibly melt the plastic. Hot glue is a hardened non-toxic glue stick that is placed in a heat-controlled gun. For styrofoam, stick to a lower melting temperature glue sticks -- warm heat instead of high heat. Hot glue is only necessary if you are attaching the styrofoam to heavy or thick items like leather, metal, vinyl and wood. Hot glue does not hold under extreme temperatures.
Model glue is made specifically for plastic models, but it works with most plastics. It is cement, which makes it a strong hold. It comes in both normal and non-toxic, is quick-drying, clear and easy to use. Other cement adhesives can be used for styrofoam as well, as long as it is solvent-free. Brands for this type of glue include Devcon, Dubro, Henkel, LePage, Super Glue Plastic-Fusion and Testors.