Streamline Light Icons. The classic iOS line icon style, with enough details and a thin line stroke. 1px stroke on a 24px grid.
Streamline Regular Icons. A minimal and geometric line style. The right balance between legibility and minimalism. 1.5px stroke on a 24px grid.
Streamline Bold Icons. A solid style for easy recognition. Bold and great to use with colors. 2px stroke on a 24px grid.
Can I match the Light, Regular, and Bold Style in the same project?
The regular weight is thicker than the light so we have a lot less space available for details (compared to the light weight). We could have just created a "light" weight with the same minimal details as the "regular" weight and make the line stroke thinner, but we decided to have a light version with more details that can be used at bigger scale, for illustrative purpose for example.
So, our decision is to have 3 different weights that have different styles based on the constraints of each weight (less space for regular, different way to design on the filled "bold" version, etc.).
Consequently, we didn't design a system of icons that you can switch between the different weights. Each weight got a different purpose and would be used in different contexts.
Good news :-)
We have now a new icon style, where icons should match better: the UI Line + Bold icons:
https://app.streamlinehq.com/icons/ui-line-pro
https://app.streamlinehq.com/icons/streamline-mini-bold