The most significant differentiator in this group is water protection. The Oppo A5 Pro carries an IP68 rating, meaning it is fully waterproof and can withstand submersion in water — a level of protection typically reserved for premium devices. The Vivo Y31 Pro 5G, by contrast, holds an IP64 rating, which only guards against water splashes from any direction, not immersion. In practical terms, the Oppo can survive an accidental drop in a sink or pool, while the Vivo offers only basic splash resistance. For users in wet environments or those prone to accidents near water, this is a meaningful real-world advantage for the Oppo.
On physical form, the Oppo A5 Pro is also the more compact and lighter device. At 194 g and 7.8 mm thick, it is noticeably lighter than the Vivo's 208 g and slightly slimmer than the Vivo's 8.1 mm. A 14-gram difference is perceptible during extended one-handed use, and the thinner profile contributes to a more premium in-hand feel. The overall volume figures reinforce this: the Oppo displaces roughly 97 cm³ versus the Vivo's 102 cm³, confirming a more compact footprint despite nearly identical height and width dimensions.
Both phones share a standard, non-rugged, non-foldable slab design, so neither caters to extreme-use scenarios beyond their respective IP ratings. Overall, the Oppo A5 Pro holds a clear edge in this group — it is lighter, slimmer, and offers substantially stronger water protection with its IP68 certification.