Signum Pro Thunderstorm is a spin-friendly string and designed for players who want easy rotation, controlled power, and a feel that is a little softer than traditional firm control polys. It falls somewhere in the middle: not a dead, board-like control string, and not a power poly that bounces like a trampoline.
I mostly tested Thunderstorm in a Wilson Blade v9 (16×19), which is a racquet I know very well. I wanted to see how it worked in a frame that is already good at control, feel, and accuracy. I also paid close attention to how it compared to the firmer control strings I usually use in the Blade.
Tech & specs
- Gauge: 1.24mm (tested) (also comes in 130mm)
- Material: Co-polyester
- Shape: Shaped / twisted profile (10 sided)
- Colour: Purple
Playtest results
Right from the first few rallies, Thunderstorm feels noticeably more lively than my typical Blade pairing. The stringbed has a clean, responsive pop, but without that harsh, metallic edge you sometimes get from stiffer shaped polys.
In the Blade v9 specifically:
- The ball comes off the stringbed a little quicker than with firmer control polys
- Launch angle is moderate-to-medium, not floaty, not laser-flat
- Spin access is easy — you don’t have to force it
- Very good control which surprised me (given its 10 sided profile)
It doesn’t feel ultra-connected, but it does feel forgiving and playable, especially when you’re slightly late or hitting on the stretch.
Break-In Period
Thunderstorm has a short break-in period.
Within the first 30–45 minutes:
- Initial firm feeling drops off
- The feel softens slightly
- Spin and depth become more predictable
After that, the string settles into what I’d describe as a stable easy-to-use window. It doesn’t have a long, flat plateau like some round control polys, but rather feels quite lively yet stable..
Durability & Tension Maintenance
For a shaped poly, Thunderstorm holds up reasonably well. Expect:
- Good performance for the first 8–10 hours
- Starts to feel slightly deadened after that (hard to describe)
- Slight loss of bite and crispness as notching increases
Tension holding is maybe above average. It’s better than very soft spin polys, but not in the same class as round control strings. In the Blade v9, I started to feel the response loosen before the string physically looked worn.
Pros & Cons
Pros
- Easy access to spin without extreme launch
- Comfortable, arm-friendly feel for a shaped poly
- Livelier and more forgiving than most control strings
- Pairs well with control-oriented racquets
- Excellent control – almost as good as some round control polys
Cons
- Tension holding is decent although not elite
- Loses some bite as it softens
- Not ideal for players who want a very firm, locked-in response
- Not really suited to touch and feel at the net (can feel dampened)
Comparable Strings
Signum Pro Thunderstorm fits alongside other playable, spin polys:
In summary
Signum Pro Thunderstorm offers good access to spin and surprisingly good control for a shaped polyester. In the Wilson Blade v9 it adds a nice touch of liveliness and forgiveness without taking away the racquet’s naturally precise feel. I think it works well for players with faster swings but don’t want a stringbed that is too hard.
As a full bed, I think it works best for intermediate to advanced baseliners who want solid spin but without losing too much precision. It is a string that won’t wow you in any particular category but rather provides a good all round option for baseline players.
Find it for purchase at Tennis Warehouse Europe (use code TNERD10 for a 10% discount).