A blade cover is a supplemental, decorative lightsaber accessory that slides over a standard, cylindrical lightsaber blade. Here are some Flame Day Blade Covers from eBay seller fire1st [AFFILIATE LINK] (he’s also on Etsy as Cosplay Covers). Full disclosure, Cosplay Covers did send me these blade covers for free to review.
Watch What is a blade cover? (Lightsaber Terminology) on YouTube
Blade covers are intended to simply cover the lightsaber blade and are not thick enough to serve as a blade by themselves. Blade covers are primarily for show and are intended to decorate or embellish the blade. Some common cool lightsaber blade cover effects include: flame (or fire), plasma, ice, etc. Blade covers are often fragile and render the lightsaber unfit for dueling.
The Flame Day Blade Covers from Cosplay Covers easily slide over the blades on the Star Wars: The Black Series Kylo Ren Force FX lightsaber and make the blades looks more ‘flaming’ and ‘unstable’.
A few different vendors on eBay and Etsy sell blade covers and some lightsaber enthusiasts will make their own blade covers as a DIY project.
There’s at least one alternate definition of a blade cover. Occasionally, someone will use the term ‘blade cover’ to refer to a ‘dust cap’. A dust cap is a PVC vinyl end cap that you attach to the open end of a lightsaber blade in order to prevent dust from collecting inside the blade. A blade cover more commonly refers to a decorative accessory that slides over the whole blade, though.
Lightsaber Blade Covers from fire1st on eBay [AFFILIATE LINK]
Lightsaber Blade Covers from Cosplay Covers on Etsy [AFFILIATE LINK]