Update README.md

README.md

@@ -60,7 +60,7 @@ We are also working with wood pulp based fabrics, that will act as filter of big
 ### Fabricating the filter
 
 Due to the density of the celulose raw material, we pulverized it and compact into a breathable filter of about 5mm thickness.
-The filter needs to be tested to evaluate its filtering capacity and porosity.
+The filter needs to be tested to evaluate its filtering capacity and porosity. The filter has three layers. 
 
 <img src="images/l1_2.jpg"  width="200" >
 <img src="images/l6.jpg"  width="200" >