These are non-relic armors made of the heaviest armor by the best smiths, magically lightened to be non-encumbering despite formidable defensive properties. Reasonably, all of these would have an additional DR+1 to DR+5 from Fortify enchantments, but that's a straightforward addition that anyone can make.
All of these are full suits, covering all locations with a uniform DR coverage. For people using the optional Joints and Heavy armor rule, assume they're using big gaps (so +2 to hit armor chinks) and lining the vulnerable bits with DR5 Very Fine, Hardened, Elven, Mithril Mail voiders (+$6375, +0.8 lbs).
Ultimate Undersuits
Any of these suits can be worn any of the other suits, depending on the wearer's preference for additional DR versus cost and weight concerns. They're sized for SM0 delvers unless otherwise stated.Cloth Undersuit: Suitable for any delver that wants a little extra protection. DR1 Very Fine, Athletic, Thieves, Giant Spider Silk Cloth Suit with Reinforced Vitals and Lighten 50%. Can be worn under any other armor without increasing bulk or giving layering penalties and adds DR1* (-1 vs pi/imp, +1 vs cut). $16552, 2.2 lbs.
Mail Undersuit: Suitable for delvers that can handle a little extra weight and a lot of extra cost for a some extra protection. Not good for delvers who have vows against wearing metal armor. DR3 Very Fine, Elven, Mithril Mail Suit with Reinforced Vitals and Lighten 50%. Can be worn under any other armor without increasing bulk or giving layering penalties and adds DR3*. $90325, 4.75 lbs.
Oversized Dragonhide Undersuit: Suitable for barbarians who want a little extra armor and protection against environmental attacks. SM+1 DR2 Very Fine, Ancient Dragonhide Suit with Reinforced Vitals and Lighten 50%. Can be worn under any other armor by SM+1 delvers without increasing bulk or giving layering penalties and adds DR2* (DR6 versus fire/heat). $43500, 6.5 lbs.
Penultimate Suits
These suits are as good as they get for the materials used, but legendary or mythic delvers can probably get access to better materials (ie, mithril mail or ancient dragon scale).Druid Ironwood Armor: A good upgrade for a rich but not filthy rich druid or faerie who can handle somewhat heavy armor but has to use organic materials or at least can't touch iron or steel. DR7 Very Fine Ironwood Suit with Reinforced Vitals and Lighten 50%. Gives DR7. $20585, 21.6 lbs. For even cheaper armor, dropping the Lighten to 25% makes this a very affordable $10635 and 32.4 lbs.
Light Dragonhide: A good upgrade for a weak or mobile delver who wants something better than leather but can't afford orichalcum or mithril. DR5 Very Fine, Athletic, Thieves', Ancient Dragonhide with Reinforced Vitals and Lighten 50%. Gives DR5* and the weight does not count for encumbrance for Fencing weapons, Stealth, Acrobatics, Climbing, etc. $35830, 7.2 lbs or $25880, 10.8 lbs with Lighten 25%.
Ultimate Suits
The suits are amazingly expensive, but are about the best armor available.Martial Artist's Robes: In some ways, this is closer to penultimate armor in protectiveness, but this is the best armor that provides the Meditative quality bonus to Chi Talent. DR5 Very Fine, Athletic, Meditative, Thieves, Giant Spider Silk Cloth Suit with Reinforced Vitals and Lighten 50%. Gives DR5* (-1 vs pi/imp, +1 vs cut), +1 to Chi Talent, and the weight does not count for encumbrance for Fencing weapons, Stealth, Acrobatics, Climbing, etc. $44650, 11 lbs.
Lightweight Orichalcum Harness: Lightweight armor for weak people who don't expect to be the focus of attacks but still need protection against explosions, shrapnel, and surprise attacks. DR7 Very Fine, Fluted, Hardened, Orichalcum Segmented Plate with Reinforced Vitals and Lighten 50%. Gives DR7 and is provides ~75 FP as a power item. $276511, 11 lbs.
Oversized Dragonscale Harness: Serious armor for a large delver who disdains civilization and likes wearing the body of his foes as armor. If the environmental protection is for cold and the armor is worn with a fire protecting dragonhide undersuit, the combined protection makes the wearer nearly invulnerable to elemental damage. SM+1 DR11 Very Fine, Ancient Dragonhide Suit with Reinforced Vitals and Lighten 50%. Gives DR11 (33 versus fire/heat). $308365, 36.4 lbs.
Mobile Warrior Armor: Powerful armor for somewhat strong delvers who fence or sneak but still want to be very protected. DR12 Very Fine, Athletic, Thieves, Elven, Hardened, Mithril Mail Suit with Reinforced Vitals and Lighten 50%. Gives DR12* and and the weight does not count for encumbrance for Fencing weapons, Stealth, Acrobatics, Climbing, etc. $350200, 19 lbs.
Fae Harness: An upgrade of the lightweight orichalcum harness for warriors who can't wear steel or holy items. DR13 Very Fine, Fluted, Hardened, Orichalcum Segmented Plate with Reinforced Vitals and Lighten 50%. Gives DR13 and is provides ~80 FP as a power item. $504950, 20 lbs.
Magehunter Harness: Armor for a strong warrior who wants to avoid magic spells affecting himself or his armor. DR13 Very Fine, Dwarven, Fluted, Hardened Plate Suit with Reinforced Vitals. Gives DR13 (Cosmic: Impenetrable versus magic) and cannot be directly affected by magic. $410865, 56.9 lbs.
Celestial Steel: Probably the ultimate armor for anyone who can afford the cost and the encumbrance. DR15 Very Fine, Dwarven, Fluted, Hardened, Celestial Steel Suit with Reinforced Vitals and Lighten 50%. Gives DR15 (Cosmic: Impenetrable by undead, demonic, or unholy powers) and glows as a daylight Continual Light spell. $594325, 32.8 lbs.
Assuming that the GM doesn't allow Fortify spells to stack, the absolute best DR possible is Celestial Steel harness with a Mail undersuit and the mithril mail voiders with a Fortify +5 enchantment somewhere: DR20+3*, $851025, 38.4 lbs. Quite an improvement from an experienced delver's heavy plate harness (DR7 plate with weak limbs, weak back, reinforced vitals, Fortify +1, Lighten 25% for DR8 at $8745, 31.6 lbs) but at 100x the cost you'd expect it to be better.