Holmes deerstalker hat: Fabric Options
For the main fabric of your hat, a thick fabric will work best to hold the shape but if you wanna go for a lighter fabric you can interface it to give it more body. Generally you want to use wools of coating weight but you can experiment with different weights and fabrics with the relevant interfacing.
A fun thing to try is printed cotton. Just double up the main fabric so each piece is double thickness. Then interface it with a medium firm interfacing.
Generally you want a lightweight fabric such as Silks or Cotton Lawn but really you can make it from any fabric you deem appropriate for lining. Just remember it needs to protect the facing and the main fabric from your head.
Depending on your main fabric’s thickness and how well it keeps its shape you may need to interface your fabric. If you are uncertain of whether your fabric requires interfacing, quickly baste your crown pieces together and see if the crown stays up right when placed on a surface. If it doesn’t it needs interfacing. As a rule of thumb you will generally need a Medium Firm Interfacing but if your fabric is quite thin you may need a firmer interfacing. If you are still uncertain you can face your crown pieces and once again baste the crown pieces together and check how it looks on your head. You can either use fusible or non-fusible interfacing. If using non-fusible interfacing you will want to flat line the interfacing to your pieces wih temporary pad stitches.
If you are trying to make a more Historical Holmes you can use Tarlatan which is a lightweight stiffened muslin. Just make sure you use natural fibres.
For the visor insert you want a firm but thin material. You may want to try either, Millinery Buckram, Plastic Canvas, Plastic Sheets or EVA Foam. You can use Leather just know that depending on depth this may create a thicker visor and may make the visor harder to close.
Just remember. All of these are recommendations. If you want to use something different go for it!