I was looking at the Riders discount ad on a supposedly light weight helmets so I googled and found this chart. Interesting, though not necessarily all inclusive list and not sure how old the info is. But, based on the list, it seems its carbon fiber or pretty much the same weight I currently have with the Shoei.
http://www.webbikeworld.com/motorcycle-helmets/motorcycle-helmet-weights.htm

Full-Face Helmet Weight Comparisons, Sorted by Weight (See Graph Below)
NOTE: Flip-up and Open Face Helmet Weights in Charts Below
See Also: Helmets sorted by shape Helmet
Size Weight (grams) Weight (lbs/oz) Shape*
HJC CL-5 Open Face (For Reference) L 1301 2 lbs. 13-7/8 oz.
BMW SportIntegral Carbon (Owner Report) L 1000 2 lbs. 2 oz. (c.)
1 Shark RSX (Owner Report) M 1350 2 lbs. 9 oz. (c.) SN
2 Akuma Phantom II MFR XL 1367 3 lbs. 0-1/8 oz. SR
3 Nexx XR1R L 1382 3 lbs. 0-3/4 oz. N
4 OGK FF-4 L 1409 3 lbs. 1-3/4 oz. SR
5 Airoh TR1 (Modular) XL 1411 3 lbs. 1-3/4 oz. R
6 Nitro N1200-VX XL 1426 3 lbs. 2-1/4 oz. SR
7 M2R MR10 XL 1426 3 lbs. 2-3/8 oz. MR
8 Airoh S4 (Enduro) XL 1445 3 lbs. 3-0 oz. R
9 Bell Mag-8 L 1445 3 lbs. 3-0 oz. SR
10 Schuberth J1 XL 1480 3 lbs. 4-1/4 oz. SN
11 Suomy Vandal XL 1486 3 lbs. 4-3/8 oz. SR
12 HJC AC-12 Carbon XL 1489 3 lbs. 4-1/2 oz. R
13 ROOF LeMans L 1492 3 lbs. 4-0 oz. R
14 CMS GP-4 XL 1495 3 lbs. 4-3/4oz. R
15 Nolan N94 Casey Stoner Replica XL 1499 3 lbs. 4-7/8 oz. SN
16 Shark RSF3 XL 1504 3 lbs. 5.0 oz. SN
17 Shoei VFX-R Air (Motocross) XL 1508 3 lbs. 5-1/4 oz. SR
18 URBAN N20 Astro L 1511 3 lbs. 5-1/4 oz. SR
19 HJC FS-15 Carbon XL 1514 3 lbs. 5-3/8 oz. SR
20 Craft RX6 Revolution L 1518 3 lbs. 5-1/2 oz. N
21 Marushin X-Moto XL 1518 3 lbs. 5-1/2 oz. N
22 ROOF Rover L 1525 3 lbs. 5-3/4 oz. R
23 AGV Stealth XL 1536 3 lbs. 6-1/4 oz. N
24 AGV K3 XL 1543 3 lbs. 6-3/8 oz. N
25 Shoei Hornet (Enduro) XL 1542 3 lbs. 6-3/8 oz. R
26 Schuberth R1 XL 1552 3 lbs. 6-3/4 oz. SN
27 Shark RSX L 1553 3 lbs. 6-3/4 oz. SR
28 ROOF Boxer (Flip-up) L 1558 3 lbs. 7-0 oz. R
29 AGV T-2 XL 1558 3 lbs. 7-0 oz. SR
30 Bell Star L 1559 3 lbs. 7-0 oz. N
31 Shark RSI XL 1565 3 lbs. 7-1/8 oz. NA
32 Vemar VSR XL 1566 3 lbs. 7-1/4 oz. N
33 SparX S-07 XL 1569 3 lbs. 7-3/8 oz. SR
34 Suomy Extreme Spec-1R XL 1570 3 lbs. 7-3/8 oz. SR
35 AFX FX-37 DS (Enduro) XL 1571 3 lbs. 7-3/8 oz. R
36 Z1R ZRP-1 XL 1572 3 lbs. 7-1/2 oz. MR
37 Fulmer D4 Evil Spell XL 1576 3 lbs. 7-5/8 oz. SN
38 Zox Azuma R XL 1578 3 lbs. 7-5/8 oz. SN
39 Nolan N43 (Modular) XL 1579 3 lbs. 7-3/4 oz. SR
40 AGV Ti-Tech Rossi XXL* 1582 3 lbs. 7-3/4 oz. N
41 Arai Vector XL 1583 3 lbs. 7-7/8 oz. SN
42 Nexx XR1R XL 1588 3 lbs. 8-0 oz. N
43 Akuma V-1 Ghost Rider L 1591 3 lbs. 8-1/8 oz. SR
44 Givi X.01 (Modular) XL 1592 3 lbs. 8-1/8 oz. R
45 Shark RSR XL 1601 3 lbs. 8-1/2 oz. R
46 Osbe X-Race XL 1601 3 lbs. 8-1/2 oz. N
47 HJC CS-R1 XL 1605 3 lbs. 8-5/8 oz. SN
48 Shoei TZ-R XL 1606 3 lbs. 8-5/8 oz. R
49 Baehr Silencer (aka FM F10) L 1607 3 lbs. 8-3/4 oz. N
50 Vemar CKQI (Modular, incl. chin bar) XL 1607 3 lbs. 8-3/4 oz. MN
51 Shoei RF-1000 XL 1610 3 lbs. 8-3/4 oz. MR
52 Xpeed XF-705 L 1611 3 lbs. 8-7/8 oz. SR
53 Caberg Trip (Flip-up) XL 1614 3 lbs. 8-7/8 oz. SR
54 OGK FF-5 XL 1614 3 lbs. 8-7/8 oz. R
55 Shark S 650 XL 1615 3 lbs. 9-0 oz. NA
56 Vega Summit II (Flip-up) XL 1615 3 lbs. 9-0 oz. N
57 KBC VR-1 L 1616 3 lbs. 9-0 oz. SN
58 Zeus ZS-806 L 1620 3 lbs. 9-1/8 oz. N
59 Bell Apex XL 1620 3 lbs. 9-1/8 oz. N
60 Bell Zephyr XL 1620 3 lbs. 9-1/8 oz. NA
61 Zeus ZS-806 XL: 1623 3 lbs. 9-1/4 oz. N
62 OGK FF-3 L 1623 3 lbs. 9-1/4 oz. R
63 Arai Quantum II XL 1624 3 lbs. 9-1/4 oz. R
64 CMS SUV Apribile (Flip-up) L 1625 3 lbs. 9-3/8 oz. SR
65 Bell Star 2010 L 1628 3 lbs. 9-3/8 oz. N
66 Akuma Stealth XL 1631 3 lbs. 9-1/2 oz. SR
67 Icon Mainframe XL 1632 3 lbs. 9-1/2 oz. SR
68 ROOF Boxer V (Flip-up) L 1638 3 lbs. 9-3/4 oz. R
69 Shoei X-Eleven XL 1635 3 lbs. 9-5/8 oz. SN
70 HJC FS-10 XL 1641 3 lbs. 9-7/8 oz. R
71 KBC Tarmac XL 1643 3 lbs. 10.0 oz. SN
72 Nexx X30 (Flip-up) XL 1649 3 lbs. 10-1/8 oz. N
73 KBC VR-2 XL 1652 3 lbs. 10-1/4 oz. SN
74 Vox Flip-up (Flip-up) XL 1652 3 lbs. 10-1/4 oz. SN
75 KBC VR-3 Stealth XL 1653 3 lbs. 10-1/4 oz. R
76 HJC IS-16 XL 1653 3 lbs. 10-1/4 oz. SR
77 Icon Airframe XL 1657 3 lbs. 10-3/8 oz. SR
78 Arai Profile XL 1658 3 lbs. 10-3/8 oz. NA
79 Craft R2 Aerospeed L 1660 3 lbs. 10-1/2 oz. SR
80 AGV Miglia (Flip-up) XL 1666 3 lbs. 10-3/4 oz. R
81 HJC Sy-Max (Flip-up) L 1667 3 lbs. 10-3/4 oz. SR
82 Arai XD3 (Enduro) L 1675 3 lbs. 11-0 oz. SN
83 GMAX GM68S XL 1677 3 lbs. 11-1/8 oz. R
84 Zeus ZS-2100 B (Enduro) XL 1680 3 lbs. 11-1/4 oz. N
85 Bell Sprint XL 1688 3 lbs. 11-1/2 oz. R
86 Arai XD (Enduro) XL 1693 3 lbs. 11-3/4 oz. SN
87 Bell Star 2010 XL 1696 3 lbs. 11-7/8 oz. N
88 HJC CL-XS (Enduro) XL 1697 3 lbs. 11-7/8 oz. R
89 HJC CL-16 XL 1702 3 lbs. 12-0 oz. SR
90 HJC CL-14 XL 1704 3 lbs. 12-1/8 oz. R
91 KBC Force RR XL 1705 3 lbs. 12-1/8 oz. SR
92 Zox Nevado R (Flip-up) XL 1706 3 lbs. 12-1/4 oz. SR
93 Schuberth C3 (Flip-up) XL 1709 3 lbs. 12-1/4 oz. R
94 Lazer Century (Flip-up) XL 1710 3 lbs. 12-3/8 oz. N
95 HJC CL-SP XL 1713 3 lbs. 12-3/8 oz. R
96 AFX FX-28 XL 1716 3 lbs. 12-1/2 oz. SR
97 Caberg Convertible (Flip-up) L 1717 3 lbs. 12-5/8 oz. N
98 Shoei Syncrotec Police (Flip-up) XL 1731 3 lbs. 13-0 oz. SR
99 Scorpion EXO-700 XL 1733 3 lbs. 13-0 oz. SN
100 Joe Rocket RKT 101 XL 1737 3 lbs. 13-1/4 oz. SR
101 Zeus ZS-508 (Flip-up) XL 1741 3 lbs. 13-1/2 oz. R
102 Shoei RF-1100 XL 1746 3 lbs. 13-5/8 oz. N
103 Fulmer AFS7 XL 1749 3 lbs. 13-3/4 oz. N
104 Vemar VSREV L 1748 3 lbs. 13-5/8 oz. SR
105 Caberg Konda (Flip-up) L 1755 3 lbs. 13-7/8 oz. SR
106 Arai Corsair V XL 1758 3 lbs. 14-0 oz. SR
107 HJC Sy-Max II (Flip-up) L 1762 3 lbs. 14-1/8 oz. SR
108 Vega Summit XPV (Flip-up) XL 1762 3 lbs. 14-1/8 oz. SR
109 Z1R Eclipse (Flip-up) XL 1765 3 lbs. 14-1/4 oz. MR
110 Shoei X-12 XL 1766 3 lb. 14-3/8 oz. N
111 AFX FX-11 Lightforce XS 1771 3 lbs. 14-1/2 oz. SN
112 Caberg Sintesi 2 (Flip-up) L 1772 3 lbs. 14-1/2 oz. SR
113 Scorpion EXO-400 XL 1785 3 lbs. 15-0 oz. SR
114 Shoei Multitec XL 1786 3 lbs. 15-0 oz. R
115 Schuberth S1 XL 1789 3 lbs. 15-1/8 oz. NA
116 Vemar VTXE XL 1790 3 lbs. 15-1/8 oz. SR
117 AFX FX-87X (Snowmobile/Street) XL 1799 3 lbs. 15-1/4 oz. R
118 HJC IS-Max (Flip-up) L/XL 1803 3 lbs. 15-5/8 oz. SR
119 Caberg Justissimo (Flip-up) L 1806 3 lbs. 15-5/8 oz. N
120 Scorpion EXO-1000 XL 1821 4 lbs. 0-1/4 oz. SN
121 Schuberth C2 (Flip-up) XL 1827 4 lbs. 0-3/8 oz. NA
122 Reevu MSX1 (2010) XL 1839 4 lbs. 0-7/8 oz. SR
123 Zeus ZS-3000B (Flip-up) XL 1842 4 lbs. 1-0 oz. SN
124 Nolan N102 (Flip-up) XL 1850 4 lbs. 1-0 oz. R
125 Nolan X-lite X-1002 (Flip-up) XL 1855 4 lbs. 1-3/8 oz. N
126 KBC FFR (Flip-up) XL 1867 4 lbs. 1-7/8 oz. N
127 Vemar Jiano (Flip-up) XL 1884 4 lbs. 2-1/2 oz. SR
128 Scorpion EXO-900 (Flip-up) L 1888 4 lbs. 2-5/8 oz. SN
129 Nolan N103 (Flip-up) XL 1891 4 lbs. 2-5/8 oz. N
130 HJC FS-Max (Flip-up) XL 1911 4 lbs. 3-3/8 oz. R
131 Zeus ZS-3000 (Flip-up) M 1924 4 lbs. 3-7/8 oz. SN
132 Shark Evoline (Flip-up/Modular) L 1928 4 lbs. 4-0 oz. SR
133 Shark Evoline Series 2 (Flip-up/Modular) L 1948 4 lbs. 4-3/4 oz. SR
134 Fulmer M1 Modus Flamethrower (Flip-up) XL 1954 4 lbs. 4-7/8 oz. SR
135 Shark Evoline (Flip-up/Modular) XL 1960 4 lbs. 5-1/8 oz. N
136 Suomy D20 (Flip-up) XL 2003 4 lbs. 5-5/8 oz. SR
137 Caberg Sintesi 2 (Flip-up) XL 2006 4 lbs. 6-3/4 oz. SR
138 Caberg Sintesi (Flip-up

This helmet got an excellent review from webBikeWorld. Does anyone have one and how is it?
http://www.webbikeworld.com/r2/motorcycle-helmet/akuma-phantom-2/
Conclusion
The Akuma Phantom II helmet shows what can be done when attention is paid to weight. The combination of light weight and the standard photochromic visor, along with the high quality fit and finish, make this one a standout
Summary: Ultra-light carbon fiber helmet is comfortable, has good air flow and is relatively quiet, considering its no-nonsense "Made For Racing" (MFR) design. Another first: the Akuma Phantom II is the first motorcycle helmet made to come with a genuine Transitions SOLFX brand photochromic visor.

Not cheap by any means, $397 (which is less than a new Shoei)was the best price I found. I think it is on my list for the future, when I replace my outdated RF1000.