Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. - Wikipedia
: a plastic substance specifically : any of numerous organic synthetic or processed materials that are mostly thermoplastic or thermosetting polymers of high molecular weight and that can be made into objects, films, or filaments -Merriam Webster
plastic, polymeric material that has the capability of being molded or shaped, usually by the application of heat and pressure. This property of plasticity, often found in combination with other special properties such as low density, low electrical conductivity, transparency, and toughness, allows plastics to be made into a great variety of products. These include tough and lightweight beverage bottles made of polyethylene terephthalate (PET), flexible garden hoses made of polyvinyl chloride (PVC), insulating food containers made of foamed polystyrene, and shatterproof windows made of polymethyl methacrylate. -Brittanica
Composites like CF and fiberglass use those materials as a stress distributing component and a plastic component as the rigid layer.
Historically fiberglass composites used things like polyester resin - a polymer derived from oil - as the rigid component.
If that's not a plastic, what is it then?
Metal? Wood? Glass?
As someone a little older than you, who's dealt with chronic pain for 30+ years and despises the gym, I'm giving you some "tough love": you're just gonna have to do it. The trick I've found is to focus on what tomorrow will look like because of what I'm doing right now (those tedious physiotherapy exercises).
But, ease up on your self-criticism, you're clearly not able to do much right now, again, having "been there" for 30+ years, you simply can't force it, you must be patient and wait until you're recovered enough from the current thing.
A couple other things that have provided tremendous improvement:
Massage from a therapist that approaches it like physiotherapy. I've had a few therapists where it was challenging to get through a session (because it's painful, just like working out or physical therapy), but each visit I'd reach a new level of flexibility/mobility and reduced pain. Which I can then maintain with my own exercise.
Yoga. Because yoga provides both flexibility and strength training simultaneously, it can be very effective. You use one set of muscles to stabilize, while stretching their complement. It has an isometric element using your own bodyweight. This guy's story has been my inspritation for years now.. As bad off as I am, he started off way worse. He gives me hope. DDP's own story of coming to yoga is also inspirational, and most of his stuff is on YouTube.
Just remember that so much in life is about doing a little bit, repeatedly and regularly, not doing a lot at once. It's better to do 15 minutes of yoga once a day than going to the gym sporadically.
You got this, you can do it.
Edit: forgot to mention a Theragun. They may seem gimmicky, but I've seen first hand how effective they can be. Be careful of the knockoffs, some really suck so much it would make you think the whole idea is bunk. There are other brands that work, I just don't know which ones. You can get the Theragun mini on sale for about $100, it's at least a known quantity. If anyone knows a good knockoff, I'm all for spending less. Just the ones I've tried have sucked (though one massage therapist has a knockoff and it works fine).