Usually used for shirts and skirts.
I’m looking to replace a number is failed headlamp head bands. The elastic is shot.
Any go-to material folks use?
Try a local fabric and craft store, like Joann, Hobby Lobby, or Michaels.
For example, here is 1 yard of black 1” wide elastic at Michaels.
They may also sell it in bulk by the foot or yard. Ask in the fabric section.
I haven’t used this material for headbands, but it seems similar to the ZebraLight and Armytek headbands I have, which are also 1” wide.
When you say “grippy,” do you mean something with a rubberized surface?
FYI, these stores almost always offer a coupon for 30% or 40% off a single item. Check the front page for a coupon that you can print or show on your phone at the register.
Here is another place you can try. They sell a lot of high end material that I have had trouble finding at places like Michael’s. They are a smaller company and I like supporting them. This should take you to the elastic section. They have a few different types of elastic with grippy material on it.
Edit: sorry I can’t get the link to work right. It keeps getting split up at the hyphen. You might can copy and paste the whole text in your browser. Just make sure there is a hyphen between ‘Narrow’ and ‘goods’
Yep, that’s the stuff- but it’s really thin. On the order of ‘I don’t want this to be seen in my skirt’ thin.
The very thick stuff used in head bands isn’t. And the ‘grippy’ part is just what you said- stuff to keep your head band from sliding down. I’ve found some that has waves, silicone, etc- but none has been thick on the order of 3 or 4mm. Mostly very thin, very light weight material.
I also figured there had to be a ‘stretch’ factor, like springs, but darn if I know where to look for it or what it’s called. 
There are all sorts of replacement headbands on Amazon.
Unless you want to make some sort of custom rig you might do a search there and see what turns up.
All the Best,
Jeff
Or check Amazon: “25 yards of 1”“:https://www.amazon.com/Yards-Elastic-Gripping-Rubber-White/dp/B06Y3S71KW, ”5 yards of 1.5”“:https://www.amazon.com/Silicone-Gripper-Elastic-Webbing-Garment/dp/B07MDJDWZ7/
Go Boilers!