These polymers decompose at high temperatures without melting and are soluble in very few solvent systems due to their rigid molecular backbone. PBO is soluble in strong protonic acids such as PPA, methane sulfonic acid (MSA), chlorosulfonic acid, and trifluoroacetic acid via backbone protonation, which weakens intermolecular interaction and facilitates dissolution. Several research groups have studied the solution properties of cis-PBO and have confirmed the high chain rigidity from the exponent value of 1.8 in the Mark–Houwink equation in MSA at 30 °C.

It has been reported to exist in anisotropic liquid crystal PBO phase in 100% sulphuric acid at 70 °C at about 5.5 wt% PBO. Polymerized lyotropic liquid crystalline PBO/PPA solutions are directly spun without polymer precipitation and redissolution via dry jet-wet spinning technique. PBO fibres are prepared using 13-17% solid content in poly-phosphoric acid solution at 60-90 °C. The structure formed during coagulation shows a network of oriented microfibrils. Heat treatment at 450-500 °C for one minute under tension results in about eight times and 10-20% improvement in modulus and strength, respectively. Similarly after high temperature treatment, the modulus of PBT fibres exhibits a remarkable improvement of 0.8-16 times while the fibre strength increases approximately by 50%. Improvement in overall axial orientation, crystal perfection and lateral order lead to improved mechanical properties. PBO fibres have been commercialized by Toyoba Co. Ltd., Japan under the trade name Zylon.

Tensile strength and modulus retention rates of PBO fibres have also been investigated under various environmental conditions such as temperature, humidity, and exposure to ultraviolet and visible light. At 400 °C, PBO fibre (Zylon HM) retains 75% of the room temperature modulus. However, high temperature with humidity has a drastic effect on strength. At 250 °C with saturated steam, the strength retention in PBO is below 20% of its room temperature value. Therefore, PBO fibres should be stored in low RH environment. PBO tensile strength also drops sharply with UV exposure in the initial stage, which indicates that the products of PBO fibre for outdoor use have to be protected from the UV radiation. Exposure to visible light also affects PBO strength. For example, one month exposure to two 35 W fluorescent lamps placed 150 cm away from the sample is reported to reduce the PBO fibre tensile strength to nearly 70% of its original value. The excellent chemical resistance to various organic solvents, acids, and bases leads to high strength retention; however, the PBO staple fibre showed low resistance under acid and base at high temperature. Besides tensile properties, fibre dimensional stability is also important for structural materials. The thermal shrinkage of PBO fibre after hot air treatment for 30 min without applying load was only about 0.2%, while under the same conditions, p-aramid and co-polyaramid exhibited about 0.5 and 0.7% shrinkage, respectively. Based on the creep testing, at 60% of the failure stress, failure time of 19 years is predicted for the Zylon HM fibre. Abrasion resistance of PBO on metal is higher than that of aramid fibres under the same load, while both the PBO and aramid exhibit much lower abrasion resistance than that of nylon or ultra high molecular weight extended polyethylene.