Thermoplastic Polyurethane is a family of plastics that are part of the much large Thermoplastic Elastomer family (TPE). TPU is listed separately from TPE as its properties and print settings are quite different. TPU was the first major elastomer that could be easily processed using thermoplastic method however it hasn't been used for 3D printing until relatively recently.
TPU has a slightly higher abrasion resistance and hardness than TPE whilst still being very flexible and very elastic. TPU also has better chemical resistance than TPE, particularly to oils and greases. TPU has similar properties to rubber, however as TPU is a thermoplastic it can be used for 3D printing.
Printing with TPU is somewhat similar to printing with TPE. It is a soft material printed at quite a high temperature (around 240°C) so adheres to itself very well. The problem faced when printing with any soft, flexible filament is that it can buckle when being pushed through the extruder, leading to blockages. The problem is slightly less severe for TPU as it is a little stiffer than its TPE counterparts.
Some TPU filaments have a number and the letter A after their name, for example TPU-98A. This is in reference to the Shore Durometer test, a measure of hardness commonly used for plastics. The effects of the test will be effected by a material's hardness and its elasticity. A Durometer rating of 98A is similar to the hardness of the wheels found on roller skates and skateboards. TPUs with different Shore Durometer ratings will have slightly different properties so it is worth comparing them to see if one is better for your intended use.
TPU is a great option for 3D printing that requires the flexibility and elasticity of TPE but needs higher resistance and durability. Here at Filaments.directory you can select the right TPU filament using our constantly updated list of suppliers and our comprehensive search tool!