It has spaces between the rows of yarn. That's also why we can see the lighter yarn that makes the shape of his mask face.
If you took a picture of him wearing it, with a special camera set to use certain wavelengths of light, you could actually see right through his balaclava.
Sony had a video camera some years back, that used this technique for ultra low light video recording, and had to change it - it had the ability to look right through some types of clothes - especially thin swim suits and knit cloth.
