Flexible air dam?
 

https://patents.google.com/patent/US4585262

I’ve seen stuff like this on big trucks(front wheel well) but is there any way to get the bristles in a pre fabricated strip? With such, we could have air dams extending to half an inch above the road for max FE benefit, not to mention using it in front fender wells where rubbing wouldn’t be a concern, as opposed to using a front wheel skirt

I found something that looks promising...

https://www.northshorecommercialdoor...-b07-flex.html

Hm, seems like air at highway speeds would still find its way through the bristles somehow and cancel some of the aero benefit, but more from a splitting hairs standpoint. Interesting material though. Why not just go with lawn edging though?

Some early 1960's small skirtless hovercraft experimented with bristles in lieu of a flexible rubberize cloth for a skirt.

As I understand it they allowed almost all of the air pressure/air flow to escape and were worthless.

A simple test to verify would be to take a broom to the gas station and shoot compressed air though it. You will find out soon enough first hand.

EDIT: Experiment closer to real life.

Have your wife drive, take a whisk broom with you out on the highway, roll down the window and feel how much air gets through.

Only a loving wife will understand your madness. :D

Admittedly I wasn’t considering the brush seal as a primary air dam, but to extend a lawn edging air dam to near ground level without all the scraping... however the prime use, IMO, would be for super low side skirts, and to fill the gaps in the wheel wells... I figure it might work a little better where it’s near parallel to airflow

The race track car discussions I've read in forums favor using conveyor belt material. In practice runs the parts that are too low get worn down by friction, then come race-time there is no friction but the spoilers are at the lowest they can be for that particular track.

Problem in comparing to street use is the variables and unexpected conditions we come across. However anyone with a low slung car knows which driveways to avoid by a glance. Still, there are always surprises.

I may have to look into the conveyor belt material... I just seen the air brush on the wheel wells of big rigs and got inspired lol

Why not both? Lawn edging as a backer for [2/3 of] the brush. Another source is aircraft hangar door seals.

As it is, the brush seal, in enough length to extend an air dam and to fill the gaps in the front wheel wells, would be the single most expensive mod on my car, by a wide margin... i don’t think the gain from using it would be huge either...

I have long wondered about using "Great Stuff" filler for a molded front wheel well shirt/fill extending the body contour as close as possible to the tire/wheel leading edge & top.