I've been looking for a flexible filament in the range of 80-90 Shore A that creates a matt finish but couldn't find anything yet.
Do any of you have tips or experiences with various filaments in this regard?
Fiberlogy do a matt flexible, it is 40 on Shore D, which roughly equates to 85 - 90 on ShoreA.
ATARAXIA ART Flexible PLA+ "Light Brown 466 C" looks and feels like a rubber band material (not as stretchy, but similar look and feel unlike the product photo): https://www.amazon.com/dp/B099QZ55PJ?psc=1&ref=ppx_yo2ov_dt_b_product_details. The material is also called Soft PLA and has existed for a long time by that name but it is difficult to use. As noted by a 2013 MatterHackers review (and in my attempts so far), Soft PLA is formless when it comes out and tends to bunch up. One review on Amazon says ATARAXIA ART Flexible PLA+ is actually 1.65 mm so using that diameter in your settings may help (or measure it and use whatever is correct). Though its Shore Hardness is 89A it is difficult or impossible to extrude consistently with Bowden, but you could try it with Bowden if you want, or try direct drive. I have to use the SiePie profile in Cura (20 mm/s, .08 layer height) and it still leaves gaps regularly. I think the finish has more drag against the sides of the Bowden tube. I use a JGAURORA A3S which has a very tight extruder--otherwise a Bowden style may need an upgraded extruder to print any flexible filaments. I have an old TECBOSS bowden tube (cut down to 680 mm; ID 1.9mm, similar to Capricorn tubing) which usually makes 85A TPU print (gloss TPU such as YOYI) consistently with the SiePie profile.
What project you working in
You can try priline I have had great results with them, but not the most flexible thing. It is still flexible enough to do really cool things with such as phone cases. No matte finish though.
SpiderMaker SpiderFlex, Shore 90A hardness, matte finish. Only comes in a couple colors and runs about $90/kilo on Amazon. Print at PLA temps (210C, no heated bed, glue stick or PEI) and TPE speeds (15 mm/s). As with all flexibles, make sure your spool mounting solution has little to no drag. For some reason they recommend using a direct drive without an all-metal hotend so I haven't run this through an E3D V6, but it does fine on a Rep2.
Try Recreus Filaflex 82A. Not fully matte. A light sanding might work.