Multi-layer composite films are currently considered one of the best materials for clear aligners in the market. The advantages of multi-layer composite films, when compared to other materials previously or currently used, include:

1. Improved Aesthetics: Multi-layer composite films provide better clarity and transparency, making them more aesthetically pleasing and less noticeable when worn by patients. This feature is highly favored by customers who prefer discreet orthodontic treatments.

2. Enhanced Mechanical Properties: The multi-layer structure of the composite films allows for more customized and controlled mechanical properties, such as flexibility, strength, and stiffness. This results in improved force transmission during orthodontic treatment, leading to more predictable and effective tooth movement. 

3. Durability and Resistance: The incorporation of various layers within the composite film offers improved durability and resistance to wear, tear, and discoloration. This ensures that the aligners maintain their strength and appearance throughout the treatment period.

4. Comfort and Fit: Multi-layer composite films provide better adaptability, ensuring a more precise and comfortable fit for the patient. This leads to increased patient satisfaction and better adherence to the treatment plan.

5. Efficient Manufacturing: Advanced manufacturing methods, such as 3D printing or injection molding, used in producing multi-layer composite films allow for greater accuracy and reduced production times. This efficiency can lead to cost savings for both manufacturers and customers. 

6. Potential for Innovation: The versatility of multi-layer composite films allows for ongoing research and development, paving the way for further innovations and improvements related to material properties and treatment outcomes. 

The technological principle behind multi-layer composite films involves the strategic combination and arrangement of various layers of materials, each contributing specific properties, to form an optimally performing film. This engineering design allows for improved control over the performance and functionality of the final product compared to single-layer materials.

In conclusion, multi-layer composite films offer significant advantages in terms of aesthetics, mechanical properties, durability, comfort, manufacturing efficiency, and innovation potential, making them a top choice for clear aligner materials.