I've learned that the fabric you would use in real life for a certain article of clothing is not the same type of fabric you might use for a scaled down 1:6 ratio character. Specifically, because of the stiff or heavy weight of the cloth.
Let's say I had characters with Jeans, a Velvet dress, a leather jacket, a sweater, a rain jacket, and cotton pajamas. What would be the materials that people commonly use that translate best to screen for these types of clothing? I've heard Shirt Denim mentioned for Jeans.
Do you just go scouting for materials and see what works best with tests?
Short answer - yes!
Jeans could be light shirt material.
Velvet more complicated, there is a faux suede that might do the job.
A leather jacket? I have a black fake leather ladies' handbag from a charity shop that I have stripped down and pulled the backing off the 'leather' this gives a thin supple material that looks pretty good. Apparently leather gloves work well too, but I can never find any.
Sweater - I have seen pics of people knitting using bodkins and embroidery wools.
Rain Jacket - thin plastic material
Pyjamas - I have an old shirt with a fine strip pattern on it, that I shall be using for a Victorian nightdress and cap. And another with a small pattern that looks good for contemporary bedding.
I use some diluted PVA to stiffen materials, also wire in the hems and ties and black wrap for collars and stiffer items. Something I hate with stopmo puppets is when clothes look like they are defying gravity. I think this makes them look like dolls and try to avoid it.
Light shirt denim works well for jeans.
I agree with Simon, look at suede fabrics for a velvet look.
There are fabrics in the quilting section that have small scale prints, though the weight of the fabric is a little heavier than ideal. I've also bought old shirts from charity shops with small scale stripes or check patterns, some are lighter fabric as well. That would probably do for pyjamas.
Sometime i get clothing made for 1:6 scale action figures. Some can be very well made, some crappy. But it is proportioned fairly realistically as far as body proportions are concerned, so wouldn't suit some non-realistic styles of puppet where you do have to make everything. (Thinking of the Boxtrolls characters for example.) My puppets do have bigger heads and hands than the true scale figures and that works ok. Actually, 1:6 shirts often have collars that are too big and look better with a larger head than with the action figures they are made for. Look under Military and Adventure in action figures at eBay, and maybe in Historical or Film & TV as well. I bought this black "leather" jacket on eBay Sorry it's too dark to see much):
Whenever possible I would use 2 way stretch fabrics for costumes. It gives you a lot more leeway and is a lot more forgiving.