EVA is a thermoplastic polymer having a distinct melting point crossing which the polymer will be in a completely molten state.  However, PVB is not a pure thermoplastic polymer and has elastomeric properties. This means that there is not a distinct melting point and cross-over to a purely molten state. When this material is heated it will become softer and softer.

Next to this, also the melt flow index (MFI) difference between both polymers is very different. MFI measures the difficulty of thermoplastic polymer melt flow. The MFI for EVA is much higher, which means that when the EVA is molten, it is also very “liquid”, whereas the PVB polymer will be in a rubbery state at higher temperature and will flow a lot less. Therefore, EVA is very suited for applications where large voids need to be filled.

Another difference in thermal properties is the glass transition temperature (Tg). For raw PVB polymers this is rather high (around 50°C) which makes PVB a brittle material. Therefore, a plasticizer is added to bring the Tg to around 6 - 20°C.  Tg for EVA is much lower, around -40°C to -30°C. This makes EVA a softer material compared to PVB at its processing temperature or in other words, EVA can have a lower processing temperature than PVB. The softness has implications on mechanical loads on one hand, but on the other hand this low Tg makes EVA very suited for (very) low temperature applications.