Overview & Obtaining
Tribalwear is the only neolithic garment in RimWorld, and covers the torso, neck, and legs. Tribalwear is also the cheapest garment to craft (other than headwear), requiring a measly 35 resources to make - making tribalwear the official budget solution to remove 'Naked' thoughts on both genders of colonist. Tribalwear can either be crafted, or stripped from Tribal raiders.
As a neolithic garment, tribalwear can be constructed at a crafting spot, or tailoring bench - the former option not requiring any research whatsoever. A piece of tribalwear requires 35 of any textile, and 54 seconds of work (3,200 ticks) to be created, assuming baseline global work speed, consciousness, sight, and manipulation.
Conclusion & Comparison
Tribalwear insulates better than a set of pants combined with a button-down shirt (10 Degrees Celsius vs. 7), but tribalwear offers absolutely no protection unless made from a material which offsets protection (e.g. Devilstrand). Additionally; armoured vests can't be worn on top of tribalwear, as tribalwear occupies the on-skin and middle slots for apparel. Therefore Tribalwear should only really be made early-game when you start getting new colonists (which may not be sufficiently clothed), and when you typically won't have many textiles in storage yet - or when in crisis where you desperately need new clothes and there are no other alternatives (extreme case).
Tribalwear is ideal for prisoners though as it offers essential bodily coverage, it's cheap, and also offers no protection: making prison breaks easier to deal with as prisoners can be downed easier (especially important through mid-late game when enemies frequently spawn with armoured vests). You can force prisoners to wear tribalwear by stripping them before capturing, and then ensuring there's a higher priority stockpile specifically for Tribalwear in their cell/barracks.
The following table(s) will display how good some normal quality Tribalwear is at insulating when made from various materials...