A look at the internal construction of a common type of low voltage LED filament that is often used to give the effect of a long coiled filament in decorative lamps.

The 300mm (12") filaments have an illuminated section of about 285mm (11") with 200 LEDs in parallel along the length, running at around 3V.  This makes them very easy to power with batteries or a USB power supply, using a couple of 10 ohm resistors in series.

In a dim room they can be run at extremely low current to get a strong visible line of colour.  Literally just a few milliamps.

Here's a link to the Aliexpress page I bought these from:-
https://www.aliexpress.com/item/1005002433050598.html

The 300mm versions should cost about £7-£10 for five including shipping.  If they hike the price, consider other suppliers.

There are other sellers with more expensive listings.  I'm not sure if the filaments they are selling are a higher spec or if it's the same ones.

If using these in a way that will allow lots of flexing, then I'd recommend reinforcing the ends with a short piece of 2.5mm heatshrink for strain relief.  If using in a costume then make sure they can be removed and replaced easily.

A link to the video that inspired me to try some of the filaments out:-
https://www.youtube.com/watch?v=zhe8d9NgcsI

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