Thermoplastics are polymers that can be reshaped if they're heated, while thermosets can't. In other words, if thermoplastics are exposed to heat, they'll melt, meaning they can be remolded into new shapes. Once you've molded thermosets, however, you're stuck with them. When heated, thermosets simply turn into charred remains.
Each type has pros and cons. Thermosets, for example, tend to be a stronger, better insulators and more durable when exposed to extreme conditions. Thermoplastics, on the other hand, are generally cheaper, easier to make and better in terms of recycling.
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