The short answer
Every USBC-approved ball must measure at least 73D on a durometer. Since 31 December 2025, high-performance balls with slow oil-absorbing covers, which bowlers know as urethane, must measure at least 78D to be approved for sale in the U.S. So a “78D” ball is a urethane ball made to the new, harder standard.
What the number measures
The “D” is the Shore D scale of a durometer, a gauge that presses a small point into the surface: the higher the number, the harder the surface. USBC’s test, from its Equipment Specifications Manual: “The average surface hardness from 10 readings around the bowling ball shall not be less than 73 when measured with the durometer D when measured at 70-77 degrees Fahrenheit.” Changing a ball’s surface hardness after it is made, for example with chemicals, “is prohibited.”
What “slow oil-absorbing” means
USBC doesn’t write “urethane” into the rule. It classifies covers by how fast they soak up oil: slow oil-absorbing covers are “coverstocks that absorb oil in 90 minutes or longer when tested with USBC’s standard operating procedure for oil absorption.” Reactive resin covers absorb lane oil faster, which is why they need regular cleaning. The 78D minimum applies to high-performance balls with the slow-absorbing kind; entry-level reactive balls and balls without high-performance cores are exempt.
Why USBC made the rule
USBC announced the change in September 2025. It gave four reasons: lane pattern integrity, competitive fairness, player development, and governance. Its announcement says these balls “can alter lane patterns more quickly” and “can measure softer over time, making it difficult to distinguish between natural aging and tampering.”
How to tell a 78D ball
From 31 December 2025, the manual requires these balls to carry an engraved 78 “around their ball series name, CG marking, or serial number engravings.” A pro shop can also check hardness with a durometer, but for an official ruling it is USBC’s own durometer that counts.
Where urethane balls are allowed
For leagues, little changes. Urethane balls approved before the rule stay on the USBC approved ball list and can still be used in certified leagues and tournaments that allow them. USBC’s national tournaments are stricter, from 1 January 2026:
| Not allowed at all (any hardness) | Allowed if 78D |
|---|---|
|
|
From USBC’s announcement. At Junior Gold, 78D balls are allowed in qualifying only, not from match play to the finals. USBC adds that balls made before 1 August 2022 are ineligible for national tournament use regardless of hardness. Check each event’s own rules before you enter.
Should you buy a urethane ball?
Storm describes urethane covers as a popular choice for spares and "playing on shorter oil patterns." Our urethane vs reactive guide covers the difference, and the ball spec table lists current urethane balls with their numbers. If you buy one new, look for the 78 engraving.
Common questions
What does 78D mean on a bowling ball?
It is a hardness reading on the Shore D durometer scale. Since 31 December 2025, USBC requires high-performance balls with slow oil-absorbing covers, which in practice means urethane balls, to measure at least 78D to be approved for sale in the U.S. Other balls must measure at least 73D.
Why did USBC make urethane balls harder?
USBC said these balls can change lane patterns more quickly and can measure softer over time, which makes natural aging hard to tell apart from tampering. It also cited competitive fairness and player development.
Can I still use my older urethane ball in league?
Previously approved urethane balls under 78D stay on USBC's approved list and can still be used in certified leagues and tournaments that allow them. USBC limited them at its national tournaments from 1 January 2026.
How do I know if my ball is 78D?
From 31 December 2025, high-performance balls with slow oil-absorbing covers must carry an engraved 78 near the ball's series name, CG marking or serial number. A pro shop can also measure hardness with a durometer.
Is my urethane ball allowed at the U.S. Open?
No. From 1 January 2026, USBC bans slow oil-absorbing high-performance balls at the U.S. Open, USBC Masters, PWBA events and several other national events regardless of hardness. 78D balls are allowed at events such as the USBC Open Championships.
Sources: USBC, Equipment Specifications and Certifications Manual (last updated March 2026): hardness specifications, slow oil-absorbing coverstock definition, oil absorption, ball markings; Dave Schroeder, “USBC announces new national tournament rules regarding slow oil-absorbing high-performance ball use”, bowl.com, 4 September 2025 (updated 23 October 2025); Storm, “The Coverstock”. Checked 29 October 2026.